Trust me, speak up whilst you can... I've just spent a year in a very tense and bitchy house ('cause we're all female and can't just smile and pretend to get along in such close quarters!). It has split a previously happy and close group down the middle - and all because we couldn't say no when the perpetrator asked if she could move in with us. Though we didn't realise that the girl in question was quite so bad until after we'd signed contracts.
So yeah, probably best to talk about it with the rest of the group - maybe they have doubts and just need someone else to bring it up.
The more time you're forced to spend with a person, the more you're going to notice their bad points - so if it's already happening...
And the trouble is, no one who doesn't have to live with a person realises how bad they are.
That said, you might just have to get to know her. Keep your friends close, keep your enemies closer.