[Ellie May]

First a question for you.
Has she been spayed and if yes, how did she do with the anesthesia?

Drinking excessive is a symptom of LS or MVD.
She was drinking double what she should've been.

It could be MVD or it could be a shunt.
Have you talked about doing a protein c test?
An ultrasound in this case would not be a terrible idea because while it is only 60-80% accurate for showing shunts, it will show if she has ammonium urate stones (instead of just crystals).

The Denamarin is good but even better would be Denosyl (Same) and instead of the marin, something like Hepato Support. Marin contains a small amount of beef liver and yeast which aren't recommended. But then, it is a very small amount. Denosyl is cheap from entirelypets.com and some use Vetri DMG instead.

If she isn't eating it means that she doesn't feel good and toxins are likely buidling up. In this case I would start lactulose immediately to see if that helps.

Vitamin E is great to give as are certain fish oils.

The K/D that some vets give does contain pork which isn't recommended.
The Royal Canin LS 14 is very palatable and may work here.

I would strongly consider going to see Dr. Center at Corness since you aren't too far away. It would be by far better than local vets.