sometimes things happen which people just need time alone to sort out, give her time, it could be that something has happened which she needs time to sort out, something which for whatever reason she feels she can not share with you this may not mean she doesn't care about you. the best thing you can do is to be there when/if she needs you in the future.
it is really hard when the people you trust turn away, look at it as a chance to try new things, meet new people, make new friends, and build new experiences. it will give you new things to talk to her about when/if she returns.