make her feel that you care about her, le her know she can trust you, and that you won't abandon her. that's the best thing you can do. also, get her away from her so called "friends", since they don't seem to care much about her.
All i can say is she's a very lucky gal to have someone that cares about her so much!! I agree with timothy, get her away from those so called 'friends' and people that put her down, u may just be saving her life.. xxxx