I have kidney disease, and I had a cat who died of kidney disease, so I think I'm in a pretty good position to tell you that the symptoms your cat is suffering do not suggest kidney disease. It would be unlikely she would have diarrhea, and it would be likely that she would be vomiting and having no appetite. The increased thirst is likely attributable to the diarhhea. Of course, I could be wrong, all organisms react differently to the same disease, and I'm certainly not trying to imply that I can diagnose your cat. But I think you can set your mind at ease that she probably does not have kidney failure. I think your vets are probably correct - she probably has nothing that should worry you - probably just a virus. Good luck and we'll hope for the best.