When I was sitting in an Al-anon meeting once, they told a story of two mother's who lost thier daughters after chosing to deal with thier daughter's addiction in two opposite ways.
Each felt emense guilt thinking that if only they had handled thier daughter's situations differently, like the other mother did, their daughters would still be with them.
I'm not a very good story teller, but the point of the story was that it wasn't what the mothers had or hadn't done for their daugters. Ultimately it is the children's choice.
You are absolutely doing your best. My thoughts and prayers are with you and your daughter. I hope and pray that she chooses life, and choses to turn away from her addictions.
No matter what someone chooses, it's nice to know that someone loves you. She knows you lover her.