Let me preface this with I am in no way a physician.

With that being said, from what I have learned about this is that you are doing the right things by taking her for help. Is she eating anything at all outside of dinner time? Have you spoke to her friends and her friends' parents? If she has an eating disorder it is likely that at least one of her friends 1) know about it and 2) may have one themselves. Although some people are very secretive (especially bulimics) about stuff like this.

What is her reaction to the physician, dietician, psychologists? There are specialized nutritionists that deal with this as well, you might want to search for a licensed nutritionist that deals with these sorts of things. Be careful with this as there is a professional license for nutritionists but anybody can call themselves one so if you go with this route ensure that they are the real deal and not some knucklehead that read a few health magazines and thinks he knows something about nutrition.