What is eating disorder treatment and how to avoid it?

My mother is forcing me to go into a residential treatment program for eating disorders. I recently spent time in the hospital because of a suicide attempt, and several episodes of self mutilation tied to my depression OCD and anxiety disorder. I have a combination of anorexia and bulemia (or so I've been told), so I eat about 500 to 800 calories per day when forced by my mother, and throw them up and take laxitives. I really don't see the problem... but whatever. What happens in treatment? I'm 5'8'' 116lbs (6 more to lose) 15 years old and I dont have my period, but who gives a damn? How can I get out of this so I don't end up fat?