First, welcome to YT! I'm sorry your SweetPea is sick
.
My Wylie has Atypical Cushings, so I know what that's like. It's a very tough disease to diagnose. So, did she have an LDDS test or ACTH Stim test to help test for Cushings? What med did they put her on? Btw, there are several different meds she can try if it's Cushings.
Are there any other symptoms at all? Ie, hair loss, muscle wasting, pot belly, heat intolerance, huge appetite...etc?
Did you take her to an Internist, btw, for the specialist vet?
The other things to look into is Diabetes Insipidus...not to be confused w/ Diabetes Mellitus. DI is more complicated to test for than DM. If DI is suspected, don't restrict water *at all*, as they can die from water restriction if they have DI.