self harm, restricting or bulimia

My heart is sore. Though I know my daughter is trying to control her purging symptoms... I realize she is now back to restricting her food intake and that she has begun to cut herself again and appears to have burned herself. The process seems to be reversing itself. I've asked her about what I've seen. She said she's working on it with her therapist. I feel horrible that she is doing this in my home and I feel powerless to help her. For a while she had been drinking and I told her that I do not have alcohol in the house for her to get drunk on. I feel that I can not ignore the any of self injurious behaviour ... so I told her that I do not like any of these behaviours and the fact that they are going on in my house and that while she is living here I feel responsibility for her well being. I told her I know that she's working on it but that I really don't like what she is doing... I am considering asking her to leave her bedroom door open at all times but then where do I go from there.... do I never leave her alone? She told me that if she wants to do these things she will find a way and do them anyway... and there is nothing I can do. I just don't know what to do ... do I set limits or do I need to try and let go and let her work on things with her therapist. Any ideas? She's planning to go back to school (out of province) and this would happen in about 6 weeks... how can I say goodbye to her and let her go off knowing she's not doing well? Do I speak about school and my current concerns about her leaving or is that putting too much pressure on her? It seems strange and counter to my intuition to even be thinking of sending her off knowing that she's not stable.