Eating disorders are psychiatric disorders. There's no such thing as an "eating disorder doctor". There are physicians who oversee ED recovery programs, but as far as being diagnosed with an eating disorder, it would've been her physician, a psychiatrist, or other mental health professional (depending on their location, some therapists, etc. do have the authority to make psych diagnoses)
There must be some angle to her totally shunning BED all of a sudden, and I'm pretty sure I know what it is. Weight loss clinics that specialize in getting people qualified for surgery do not want eating-disordered patients because the surgery is more likely to fail in terms of long-term weight loss goals; and with BED in particular there's the possibility of the fatty blowing out their new gut and dying.
That's not to say that people with BED never get approved for surgery, it happens. But it's one of those things that these programs don't like. They are also likely to deny people who smoke, for example. It depends on whoever the surgeons are that are working in the program. For a time, part of my job was processing claims for this kind of shit.