MY BEST FRIEND IS SELF HARMING!?

Well the fact is, in these situations, it can only get worse. You need to tell someone, and at first although she will resent you for it, someone needs to be aware. If she is self harming, she may one day just cut too deep- and you will be so guilty, knowing you knew and could have helped her. You need to talk to her parents, and if they won't listen, your parents/teachers. People need to know, so they can help her.