It's really hard to help people that do not want to be helped. I think the best thing that you can do is be honest with your friend and tell her how you feel, tell her you are concerned about her and why. When you do that, focus on her behaviors. Things that are undeniable, like cutting herself, or restricting what she eats. Behaviors are easier to point out than feelings or thoughts, and odd behaviors are usually a sign of something else being wrong. Has she ever been to therapy?
I hope I'm not being intrusive.
Take care,
Roski