Maybe this person does need some professional help; it could even be sexual abuse. If you're afraid that she'll be mad at you for telling someone, it's better if she's mad at you, than if she doesn't get any help at all. She may be mad for a while, even for a few years, but I think in the end she'll thank you. Try contacting a church or pastor. They're usually good about keeping things confidential unless it's a matter about going to the police, like physical abuse in the home. It may also be something about school. Maybe some people are daring her to hurt herself. Maybe she's wanting to kill herself, but just can't, and so she hurts herself instead. It could be any number of things. If you really love your friend, you HAVE to go to someone. You could even go to your parents or a really close family friend for help.
Well moments ago, i had my friend in college talk to her. My college friend has been through this and she has cut her arms before. So i trust her to know what she's doing with my friend. So my college friend is currently handling this business. She can hate me for the rest of my life but i just don't want her to be hurt.