Scratching arms

I don't know what to do anymore. 

My 17 y.o keeps scratching her arms. It started 2 weeks ago during an incident and it was a self harm behaviour. Now its not self harm but just the healing process going round in a viscious cycle now. 

We bandaged it up, she took the bandage off after a few days, it was healing and scabbing and became itchy. She then kept itching it and it was all open again. So we put the bandage back on. 

We used a self adhesive dressing on one arm and she is scratching over it which isn't helping. The other arm is the bandage with is harder to scratch. I don't want to put both wrist supports on her again but may have to. 

One arm now has a scar. What can we do now?