My heart is with you. Have you consulted another vet? Don’t give up on her but please make sure she isn’t suffering. She may have swallowed something so has she had x-rays? She may have a blockage. I wish I was there to help you!
The clinic had multiple vets consulting on her case, because they were perplexed. They came to a diagnosis by ruling out everything else.
As I was in the waiting room looking over the invoice, it occurred to me that she had a battery of tests that would have cost me a fortune and a half if I was the one getting them!