I have two daughters who suffer with this. One has it under control and is doing really well, but it is a battle for her and always will be. The other has me worried and scared right now. One thing you need to know is - your daughter will lie, lie, lie to you. Do not take her word on anything to do with this problem - that includes drugs. She is probably taking diet pills and diuretics.
You need to let her know of your love for her, and that you approve of her no matter what. She will find her balance eventually, but you need to be watchful and loving to help her survive until then.
She may be using the computer to find friends to share experiences and encourage the problem. Watch that - that can be dangerous.
Good luck and God bless!
My daughter researched the effects of eating disorders on nutrition in a body. She found websites that PROMOTE eating disorders like bulimia, anorexia. Disturbing, so watch that too.
Thank you, for the blessings and thoughts.