I'd say have a look at Bryonia as a complementary too, and see what your other vet friends think. I really wish I could see more myself, but it would be only be guessing. The dehydration does seem a major concern so I'm drawn to remedies with 'internal dryness' as well as emaciation. The level of recent(?) increased irritability and restlessness may be a couple of pointers too.
What would be the physiological reason for that level of dehydration, do you know? Would it be the intestinal bacterial overgrowth or organ pathology?