caveat to post: i am not in the medical field....
dan, the thyroid issue is a HUGE factor, and possibly the only factor here. the thyroid regulates metabolism.
have her keep a super meticulous log of her food intake and workout time/intesity. take it to her doc and he can decide if her meds need adjusting. (without the log he may blow her off. every doc hearss" i'm dieting and exercising and i'm not losing any weight")