I think you should talk to her, and try to get her to see someone. Make sure she knows you're there for her no matter what, and that maybe she could call you if she feels that way, instead of cutting?
Great advice there. My best friend was doing the same thing and she said she got a counselor. Unfortunately she moved two years ago and I really couldn't do anything to see her or help her. I felt so helpless Then she told me she is seeing a counselor. She moved 2-3 hours away.

All my advice is to you is Don't give up, if you have to tell someone that CAN help her, please do so, she may be mad at you but trust me she'll thank you in the end. ((((big hugs to you))))).