Daughter dealing with ED- not sure how to handle

[Wib1]

I haven't been on here in ages, but I feel the need to be here now because the stress of what I'm dealing with is killing me.
I have an adopted seventeen year old daughter who left our home almost a year ago now because she was angry with us, and probably because she had no desire to have anyone "control" her.

She has since been engaging in increasingly destructive behavior that is going to get her in some serious trouble very shortly. She was a high achiever, a beautiful and very talented young lady with a bubbly personality, but she is also the most stubborn and defiant child I have ever met. We believe that she is dealing with some form of eating disorder, although not necessarily to the point of dangerous to her life, it is very troubling. It is hurting our family. Her selfish behavior is now also hurting her birth family, who she met just shortly before moving out. She has NO respect for anyone, least of all me. She has told me that she loves everyone else... just not me. This was devastating, but I'm not buying into the lies that she's telling herself.
She has run away from where she was staying and ran to an uncle's house. Instead of risking her safety on a 20+ hour bus ride home immediately, we opted to get her home by plane a few days later. The grandmother came unglued on me! She is livid that I would dare give her positive reinforcement for running away. I don't think she needs punishment... I think she needs help. I can already see that the natural consequences for her behavior will be alienation of her family and friends.... all of them.
I am seeking advice as to how to deal with the grandma... who to turn to, and how to handle this. At this point... I have no influence but the stress is doing a number on me.