The doctor says that just the clue that she has good days means that she is at no harm.
Actually this experience is extremely common in any number of serious diseases.
IME the majority of general peds will say what you heard, to parapharase, the only problem is in Mom's head,
when they've run out of ideas. So, you're right, time to move on, you won't get much more where you're at.
Ped. endocrinologists tend to be even more "stuck in the box" & unwilling to treat by symptoms than endos for grownups are. Hopefully there are a few exceptions to this rule.
The time-honored methods we use as adults to find a new doc are:
1) networking in our community for patient/parent testimonials. The mother-of-a-friend-of-an-acquaintance sort of thing.
2) telephone interviews/screening with a short list of selected questions.
3) researching lists of specialists. A public library reference librarian may be able to find you a list of researchers and/or specialists in the USA who might be interested in your daughter's case.
4) consider Mayo & similar diagnostic-specialty facilities
5) when failed repeatedly by conventional medicine, many adults turn to naturopathic or DO doctors with good results, but how many of them see kids?
Hopefully there will be other good advice forthcoming from the group.