Case for modernity: In Agnes Grey, the idea of choosing a plain governess as a heroine to highlight the issues of suffering governesses. The Victorians were the ones who popularised the novel as engine for social issues. In Mansfield Park we hear a little, which anticipates the Victorians, but it was not yet fully developed in the Regency era. Possibly an early example of a suffering governess is Jane Fairfax in Emma but we never hear her thoughts. She is a marginalised member of society, and ignored by that horrible snob of a heroine, Emma Woodhouse. (I've thought it is so curious how different Fanny Price and Emma are from each other, and how could Austen sympathise with both heroines). Making the underdog a heroine is also a more modern concept. Yes, I hear you scream "But what about the classic literary orphans who morph into swans?" Yes, we've heard of that nice quiet heroine who is despised for being countrified, but such heroines are normally pretty and morph into swans and become admired and fit in better with time. Agnes Grey is not one of those. She gains more knowledge but nothing is mentioned of her beauty. She does gain an admirer, Mr Weston, but he is attracted to her modesty and deepness. Rosalie's descent into an unhappy marriage is almost tragic, whereas in earlier fictions it would be satirised and caricatured, and wouldn't play a significant part of Agnes' life. Anne was quite a reclusive personality, and her own pupil's forced engagement was one of the more important events in her life. She hardly went anywhere, and after her governessship and writing career had even less contact with society. We like to call Emily the recluse but Anne was one as well. If Emily hadn't been the chief Victorian recluse it is possible Anne would have stood out.
Agnes herself is quite an independent young woman. When her father loses his money in speculation, she offers to go out to become a governess. The family thinks her nerves cannot take it. She says "Try me," and succeeds to some extent. This is something, because as a member of the gentry she is not expected to work. Mind you the families she teaches don't fall at her feet. This again is harsh realism, not the wonders an 18th century heroine would work on reforming and getting everyone's love.
In Tenant of Wildfell Hall, the escape of a wife from a drunken husband is itself radical. Not only that, she takes her child with her. Those days husbands had custody of children so Helen's flight is spectacular. Like Anne, she even tries to earn her own living by painting landscapes (though her brother generously offers her a home for free). She insists on paying him back, as well as Gilbert when he gives her a book to read, because she hates to feel obliged to anyone. Does this remind you of Jane Eyre? In those days it wouldn't have been expected for Helen to pay back her brother, which makes this startlingly modern. Also you must have noticed that Huntingdon never reforms, unlike the sickly sweet sentimental 18th century novels. This is true realism, the nitty-gritty.
Even more, she falls in love with a man while still married to her husband. This was radical. I know the Victorians had these plots, but they were more late-Victorian, and besides these sort of women were fallen women. Helen remains virtuous throughout and avoids Gilbert Markham because she doesn't want to commit adultery. Oh, and when her husband dies she proposes to Gilbert, who by the way is several social classes below her, even though he is an educated farmer. Helen is of the gentry, and her husband's death has made her well-off and the owner of a decent estate, better off than when she was a young girl. Gilbert is middle-class. Note that championing the middle-classes instead of the profligate gentry rakes in the novel is a Victorian thing. The Regency era loved the upper classes. Anne does not, because her hero isn't, and her heroine practises middle-class values such as personally teaching her own son when they can afford a governess. It was customary to hire a governess or send the kid off to school if you were upper-class.
Case for old-fashionedness: Apart from the morality tale it was meant to be (as Anne wrote in the preface, something popular in the 18th century and Regency era, just look at Fanny Burney and Jane Austen), the scene is set in the 1820's, 20 years before publication. To us, perhaps 20 years isn't much, I mean setting a novel in the 1980's and 90's isn't really historical fiction, but to the Victorians the Regency and the Victorians were vastly different. In fact they were ashamed of their Regency ancestors who were profligate wastrels and adulterers. £5000 isn't much in the Regency era according to their novels, but it is a good sum in the Victorian era, despite inflation, which shows you how prudence was exercised. The rakes, Arthur Huntingdon, would-be adulterer Walter Hargreave and the profligate son of a banker Mr Hattersley love drinking and carousing - caricatures you will find in 18th century fiction. This sort of thing was despised in the Victorian era, less reviled in the earlier days. It is not surprising to see this in Anne's fiction, because the Brontë children had access to Pamela by Samuel Richardson, which has a rake as an antihero-villain, who reforms because of a good woman. By the way I hate that book. In her preface, Anne writes:
I would not be understood to suppose that the proceedings of the unhappy scapegrace, with his few profligate companions I have here introduced, are a specimen of the common practices of society - the case is an extreme one, as I trusted none would fail to perceive; but I know that such characters do exist, and if I have warned one rash youth from following in their steps, or prevented one thoughtless girl from falling into the very natural error of my heroine, the book has not been written in vain.Anne's purpose, then, is to discourage girls from thinking they can reform a rake by marrying them - the sort of claptrap you get in 18th century novels. This opinion is modern, the setting old-fashioned. There is no important gentleman character who is respectable except Frederick Lawrence, and this is rather un-Victorian, who loved their respectable men. Even the unsympathetic characters you find in other Victorian novels are more respectable: they either have a proper job, or if they don't work, you don't see adultery and all the heinous nonsense the gentlemen here talk about.
Despite all the anti-Byronic rake sentiment, Anne's heroine is a mystery woman - yet another Gothic heritage. She says little about her past and keeps to herself. Arguably the individualistic protagonist only became fully developed in the Victorian era which makes it modernist (Frankenstein, which has got an individualistic hero, was ahead of its time, and doesn't really count. It is an excellent speculative fiction but purists wouldn't call it strictly literary though it is a classic. I think Mary Shelley would have been like a scifi author with wider themes. Also, the lack of truly convincing characters makes it not so literary. But I digress).
I sense a hint of Fanny Burney (late 18th century) in Anne, however. The epistolary form, found in Evelina, the morality as well, the presence of minor characters who take part in the plot, for example Millicent Hattersley, Helen's close friend who is about her age. Victorian heroines' close friends their age tend to be glossed over, because Victorian authors will dwell on social issues, or typicakl domestic scenes, or the inner anguish. Friends of the heroine seem irrelevant in the heroine's existence, unless they're involved in the plot as well. Millicent is different from traditional 18th century heroine's best friends because she clearly suffers inwardly, rather than act as confidant or social critic with the heroine, or fellow-gossiper. But she is not a major character, and her part in the plot, though existent, doesn't really affect the novel much.
There is even divorce mentioned, something very uncommon in a Victorian classic (until Thomas Hardy came along years later). In Regency novels you do hear divorce, which could only be available if the wife was proven to commit adultery. See Sense and Sensibility, Mansfield Park and Maria Edgworth's Patronage. The characters openly talk about divorces in high society and delight in scandal - the Victorians didn't, even though divorce was more readily available to the middle-class Victorian. Yet there is less divorce in the Victorian novels, because they were censored and repressed. Divorce was also more of an aristocratic thing because high society women tended to adulter more prominently compared to the middle-classes who wished to preserve their reputation. It was the way to enter good society, since they didn't have birth or much education or contacts. Chastity is essentially a middle-class virtue back then. Yet in Tenant, Lady Lowborough commits adultery and is divorced by her husband. Tenant is steaming full of undescribed sex, something you wouldn't expect in demure Anne Brontë, who while being paid attention by Willie Weightman:
He sits opposite Anne at church sighing softly and looking out of the corners of his eyes to win her attention - and Anne is so quiet, her look so downcast - they are a picture .On the other hand you could say divorce is modern, because it is a late-Victorian thing and after. But the fact the Brontës lived in the Romantic era and read the silver-fork fiction of that time with all its rakes shows. Anne may be a realist but she is also a nostalgic. Though differently from Charlotte who waxes lyrical over the good old days. Anne seems to be pointing to a future which is far more progressive than the good old days. Quintessentially Victorian. I don't know why she chose that era in particular, unless she wished to show how far we've progressed, or perhaps she was just more familiar with the modes of that era which influenced her childhood writings.
There's also the rationalist streak in Anne. Realism is a Victorian rather than Regency thing, but surprise surprise high passion and Romanticism in mainstream literary fiction is Victorian, not Regency, though the Regency coincided with the Romantic movement. So while she writes of rakes faithfully, Anne doesn't emphasise on high passions, what Helen felt for Huntingdon before she married him. It is reason and morality, not so much feeling that is important - lessons you will learn in 18th century novels. Victorian suitors tend to be more romantic than their 18th century counterparts, who are boring paragons of respectability who say the lady in question is good and suits him, whereas the Victorian gentleman will actually express his intense feelings for the lady and go into a melancholy when the lady doesn't respond favourably. Gilbert is melancholy when Helen rejects him, but their so-called romantic scene owes a great deal to respectable behaviour (Gilbert thinks she is smart, and hates female gossips, and Helen likes him because he is kind) rather than soulmate material. Anne was very religious so this makes sense. But it makes love a kind of morality lessons rather than high elevated feelings. Perhaps I'm biased though. It just occurred to me I didn't mention Agnes Grey in this argument. Agnes loves Mr Weston for being kind to her and dogs, and Mr Weston likes her because she is humble and not superficial. This is probably the sort of love Anne felt for Willie Weightman, who was a kind curate, a gentle mild love based on reason and respect. The passion Anne felt however is not emphasised in the novel.
Anne being extremely religious shows this up not only by getting Agnes to marry a clergyman, but by writing and having her own hymns published - before Charlotte became a published author. Yup, that's right. Old-fashioned morality perhaps, though arguably the early Victorians had their own extreme religious movements and Anne had some involvement in one of the religious speakers. Secularity and agnosticism was undoubtedly a new thing. Let's just say the educated intellectuals became more secular (though still respectable) whereas the descendants of aristocratic rakes (and rakes don't really go for religion) became more religious and respectable. There is no real answer.
Poetry-wise, she and Charlotte were intensely personal (apart from the hymns she wrote), where first-person is favoured, and the poet identifies with an individual who gives a speech. This is the dramatic form, the sort that Robert Browning popularised. Which was rather modern. But the forms was already present in the Romantic poets, so it is hard to tell.
So is Anne old or new? The answer is both. Compared to her more famous sister Charlotte, Anne's social themes are radical, but when it comes to style (and expressing the individual) Charlotte was the radical.