Hi moresparklesplease:
I'm presuming you DD is in Year 1. Toward the end of Year 1 there seems to be a settling of the pecking order and sometimes girls can be truly unpleasant. Sadly, this can continue well into Y2. (Also sadly - this also plays out amongst boys as well)
My advice is this - actually people like kind, happy people. It isn't necessary that they're outgoing.
I would stress though to your DD that she shouldn't worry too much about being friends with the 'popular' crowd if there are a lot of pre-conditions - you have to always play what they want you to play, you're being pressured to bring in gifts/ toys for them, they frequently say mean things to you, etc...
I think you should just generally be picking up on who strikes you as a really nice child - not just well spoken, well dressed, bright, etc... - but who seems really sweet. Don't insist your DD is friends, just say isn't x lovely. It will signal you approve and give permission for that friendship.
However, no matter what you might want for your child, remember that 7 is approaching and that his/ her personality will be largely set by age 7 (not that changes can't be made - but general tendencies - confidence, shyness, prone to being upset, prone to worry, etc... are likely to be lifelong traits (if you haven't followed the amazing series 7up you really should - not just because of the shocking predictor of socio-economic immobility - you can catch up with the children at 56 here: www.itv.com/itvplayer/video/?Filter=317439).
I have a very shy DH who's very slow to get used to new people/ places and prefers dealing with small numbers of people. But with that shyness, he's kind, sensitive and hugely understanding of our children when they find new situations intimidating. I wouldn't change him for the world.