beating an disorder is not really possible unless the person wants help, but, another way to go about geting her to recognize that this might be a problem would be to try a nutrionist first....it sounds a bit less intimidating. if they say that she is malnurished maybe it will spark something with her. but honestly, talk to her. tell her your concerns, dont be forceful or stern but staying quiet and watching her do this to herself isn't going to help either...she might know somewhere inside her that this isn't good, but cant admit to it by herself, and for years it has been getting worse...it might be time to try something knew to see if it can get better. I know that you are in an impossible position...it is so hard whether to just let it play out or interfer, but you tried to let it play out...so the question is do you want to give it more time or get a knew game plan. best of luck to you and your daughter.
oh, it also could be an OCD issue...if she has become freaked of the contamination of the stuff in the food....but its hard to say because the two already overlap a lot.