Hi Patagonia. wish I had a simple answer. One person I know has support groups and therapists that help them stay away from self harm. Some people respond to medicine therapy to help them stay stable.
This article may be of interest.
Self-Harm: The Myths & the Facts | Embracing Balance
The therapist and psychiatrist can be the ones to deal with this. Having your daughter supported may make your responsibility seem less.
Be careful to do self care so you do not find yourself struggling with the same behaviors.