I also harm myself (in many ways). Have you sat down and had a conversation with her about what brings her to do this? I'm guessing she feels lonely and has a lot of self hatred or guilt. This is something that is extremely hard to deal with and completely put an end to. I would just suggest showing her an endless amount of care and concern. Let her know that you love her as often as you can. Hug her..Hold her. She needs to feel cared for. This will take so much time. Patience and understanding are key.

Very true, and just ask her what you can do for her, to make her some tea, run a bubble bath, play video games, go skate boarding, take up a dance class together or karate, rent a movie, have a date night just the 2 of you.