Are you seeing a general vet, or a GI specialist? For this, I'd see a GI Vet asap bc this is complicated. I feel so bad for her, and for you too! The poor little girl, she must feel awful being so bloated like that.
Also, please read the description for Cushings...any chance she has these other symptoms too? Symptoms are about 1/3rd down the page:
Cushing’s Disease Summary (many many vets miss the diagnosis of Cushings)
And btw, welcome to YT
!