My friend cuts herself, can someone help with this question..?

[funactress12]

My best friend cuts herself. A lot. She shows me the scars and all I can do is stand there and be quiet. It sickens me. To see all the scars from her cuts. She tells me when she cuts herself and when she is going to. I read her twitter posts and half of them are about cutting herself. This is serious. I've told her that she needs to stop and all she says is it helps ease away pain, but the only thing this does is give her more pain. I really need some advice as to what to do. Please and thank you.