I am a recovering cutter.

Well When I use to cut I would do it to cover up the pain I had inside. To cope with the pain of the loneliness or emptiness. I also cut out of impulse not realizing I was doing it until I was done. I was seeing a doctor once a week but it didnt help until I decided to change the way i was living. I was also Diagnoised with depression and ptsd ( post tramatic stress dissorder).
After I started to recieve treatment And Meds I didnt have the impulse to do as often.
I also found the kind of music I listen to attributed to the cutting mood.
Writing and drawing was a great way for me to express the way i was feeling inside with out hurting myself.

I got so bad at one point that I was hospitalized I just hope that it doesnt have to come down to that with your daughter, But it did help me.

Keep a close eye on her. I know I caused my parents while i was in this state but at the time I had no clue and I thought they were out to make me even more miserable.

Help her express how she is feeling and help her find something that she enjoys.

If you have any more questiona on understanding Self Mutalation Just ask I will be happy to answer anything you throw my way.
God bless and I hope I have helped you in some way.