OMG Kim
! I am so sorry Hallie is sick, that poor darling.
It sounds like you're on the right track, and Internists are wonderful to consult during these complicated times (that's what I did w/ Wylie's Cushing's/thyroid etc). Bc of her polyuria/polydipsia - did they mention Cushings at all? Bc those other blood levels can be off w/ undiagnosed Cushings as well. If they do think there is a chance of Cushings, the first step would be Urine cortisol-creatinine ratio - but the urine MUST be caught at home, while the dog is not stressed. Just something to think about.
Please email me here or at my personal address if you need ANYTHING. Hugs and love to you and the babies!