My heart is breaking for your little girl.
Do you take her to a childrens hospital or just a ped. at the clinic? I would advise a childrens hospital in a large city, if you haven't done so already. Nothing against a good ped doc but this stuff is usually way over thier head.
Surgery may be the only answer if things don't get better. If that is the case, do not under any circumstances allow any dr's other than a very good childrens hospital due the surgery.
Have you tried pedalite? It has electrolytes in it and is made for children.
I hope that I don't offend, I will say a prayer for your daughter's good health.