Kudos to you for pursuing after the med community to get answers!!
Glad to hear she is doing much better, gaining weight and coming around.
Here is another weight gain problem.
I just went through nearly 2 yrs of battling socialized med and finally went private for resolution. Couldn't get any GP's to listen and mostly ignored or turned away from getting any help.
In our case DS-G had the problem with food, couldn't swallow, gag and spit back out food. He rarely gained weight and maybe a few ozs each month. He's always had problems breathing, day version of sleep apnea, holding his breath, couldn't control it. The response from GP's about his breathing "he should be a scuba diver!" Instead of helping, insulted us!
Problem: Enlarged Adenoids. Finally had the surgery and now he eats everything in sight and can breath normally. I'd read that this problem (Enlarged Adenoids) can stunt growth and weight gain. (BTW the Surgeon was 'stunned' at the size of his Adenoids, calling them impressive. It clicked with him that I had been pursuing a serious problem for my Son all along.)