What should I do? I can hardly stand my friend anymore?

I have a group of friends (about 9 people) that all hang out - some of us are closer than others but we all get along quite well. One of my closer friends is a girl who arrived at our school around 3 years ago. She's from Asia and speaks good english (sometimes gets her punctuation mixed up but other than that she's fluent) and is into shopping and all the rest (basically girly stuff). We have been friends for about two years now but she's kinda beginning to annoy me. She's a bit immature and doesn't know much about sex and all that grosses her out heaps and thats ok... but we're all 15 and she is really hard to talk to about boys or alcohol or whatever because she just says 'ewwww...' and changes the subject to something about shoes or she gets pissed off for whatever reason. She can be a really good friend but all this is really annoying me... what should I do because I find it hard to be good friends with her now because I would feel mean to ditch her or even stop hanging out with her as much. And I know she'll grow up but she says she doesn't even want children or to kiss or date a guy and the thought of drugs would shock her (not that I do drugs but talking about it....) - it is kinda dragging me down with my teenagehood, I guess. Advice please? xx