"Mwahahaha! I, the clumsy schoolgirl, snagged the most eligible bachelor in town!"
Bella is also liable to be perceived as snobbish and dismissive of anyone who isn't Edward, as well as being anti-social. We will come to the question of antisociability later. The fact she is pliable in the hands of Alice Cullen shows you that Bella is soft-hearted, and the fact Alice loves her (rather than be dazzled by her, like the rest of the schoolgirls) shows Bella's hidden depths, otherwise quite invisible to the luckless readers. To follow Mrs Meyer's example, always have a nurturing mother figure take a shine to the awkward heroine. Who can trust the impressions of other schoolgirls? Who are likely to see the heroine as a pretty freak or something to idolise. The clumsy heroine is also unlikely to get things done, having no leadership skills, so the mother figure is there to aid the plot. Another extension of the idea is the hero's parents love the heroine thinking she is good for him. This is to shut up the doubts of any cynical reader. Furthermore those critics who claim the heroine is a Mary Sue will instantly be deterred, because the Mother Figure is even more perfect than the heroine. She is elegant, she never makes a social error, she has many sophisticated friends who instantly take to the heroine.
But why not simply make her more accessible to her peers? you ask. Yes, but we're supposed to convey the impression she's unimpressive, shy and awkward, so the reader will sympathise with the heroine. We can't make her too unlikeable, so in comes the Mother Figure. The idea is she is Too Good, Too Deep, and Too Profound for her peers to understand her. Only those equal to her level can be her friends, namely the Mother Figure and the Hero's Parents. Making her mix only with the high-class elite also satisfies the fantasies of readers who wish to be accepted by sophisticated intelligent people. You are who you mix with, so if the heroine's friends are rich, cool and sophisticated, therefore the heroine is cool and sophisticated. We can't make her rich, because that would not make her sympathetic but all her bosom friends are. It marks the triumph of social ascent. Don't we all love that, my dearies? (this should be uttered with a leer).
No love story is entirely addictive without the Conflict, which I have discussed (in the hero), but here the conflict is that the heroine's parents are against the gloomy heroine whom they think is a Bad Influence. Despite him being rich, popular and educated and never having committed a crime in his life. This is useful so you can introduce a Balcony Scene, a variation of "Oh where art thou Romeo?" "I have come for thee Juliet!" (these lines I made up) of Forbidden Love. Instead of the rich despising the poor, it is the poor despising the rich, yet another wishful fantasy I am sure you love to indulge in.
In My Immortal, Ebony has a group of fellow Goths who are her bosom pals and who centre around her. This dispels the myth that the Goth heroine is a self-centred brat, because everyone else who matters loves her. A bevy of girls may surround her, and they all want to be like her. There must also be a popular kid who picks on the heroine, to show how unlucky she is.The popular kid will be upstaged by the heroine, because Good Triumphs in the End.
Not forgetting the String of Suitors. They are all madly in love with the heroine (Ebony screws Draco, Harry, and Voldemort, some in public, and unfulfilled lustbags include Snap, Loopin, Hargrid, Snaketail and Tom Rid). This shows you how humble the heroine is to say she's plain but so many people fancy her. You should not omit the Male Friend of the Opposite Sex (in Allo Allo, Herr Flick disguises as a "Female Secretary of the Opposite Sex"). This male friend is platonic. His purpose is to be a backup assuming you choose not the include the bevy of female friends in the heroine's circle. To show how shallow and jealous other women are of the heroine, she may be disliked by them, but to provide her with a social circle, put in a few guys. Having many friends of the opposite gender also makes you look cool and unique. For some reason outgoing male characters are supposed to be cool and make the heroine look cool as well. Especially if they do things like gourmet cookery or fencing or something.
I have forgotten to add to the why shouldn't the heroine be friendly with the others apart from the Elite. Apart from them being supposedly stupid and shallow, it is a way to tell the readers the heroine can afford to be picky about who she mixes with - yet another fantasy of many many women who hope to be snobbish but haven't the charm to do so - and get away with it.