hello withit,
I'm sorry that this problem has come upon you, but as others have said i don't believe it can be entirely reversed. Trying to reduce the severity of the situation or potential situation would be the best course of action (imo).

Regarding what others have said about encouragement, though, my advice is different. I'm an adolescent so perhaps i understand some of where your daughter is right now and in my personal case encouragement only made me want to diet more. Perhaps that's a sort of compulsive behavior in itself: where recieving praise for good qualities only fuels the desire to be even better. I'm not by any means saying don't encourage your daughter, but try to do so with caution. Pay close attention to her reactions (e.g. whether she appears defiant towards the praise or not).
good luck with everything!