As a former cutter (and stubber), for me the great turnaround came through therapy, but looking back on myself as a young person... I was under a great deal of pressure from all sides, and my eating disorder ("You can do all you like to try and control me, and get in the way of what I want to do with my life - but I can be the size I want") and the cutting were both a safety valve which, in a perverse sort of way, kept my sanity.
I used to get up in the morning, my mind a mass of confusion and experiencing a general sense of unreality, and the stinging pain of cutting made everything feel "real" again - and I could carry on with my studies, no problem.
Freetosmile - her cutting isn't about you. It's her own way of coping right now, and hopefully she will find a better one through therapy. It may take a while, and if she could articulate her thoughts and feelings in a way she could communicate to others, she probably wouldn't need to cut.
You are being very brave, and doing the best thing, by not applying any more pressure to her. That would only exacerbate the problem.
I'm very concerned at how upset and full of guilt you feel, too. As I say, this isn't about you. (((HUGE HUGS))) and hope you all get through this OK.