Support her and be there for her. Be thankful shes still a minor. She can get clean now while shes still in your care. My cousin is 23 now and has been in and out of rehab. The problem is since shes over 18 she can check herself out whenever and my aunt cannot call and check on her. She can only talk to her if my cousin calls her. Since your daughter is still a minor though pretty much whatever you and her father decide on goes. (Assuming you have joint custody).