I have some experience with this as my old girl Poopy, who died in 2010 at the age of close to 20 (I found her as an adult so her true age was always a question mark), had kidney disease too. Its complications did eventually claim her life but I kept her alive and happy for many years after the diagnosis.
Lil, it is SO IMPORTANT that cats with kidney disease eat, even if it's crap Fancy Feast, something is better than nothing. The highest quality prescription food available won't help a cat if she won't eat it. Get her whatever she wants!
Here's a wonderful website that helped me so much when I was coping with my Poopy's kidney disease, and I know it will help you as well:
Tanya's Comprehensive Guide to Feline Chronic Kidney Disease - Everything You Need to Know to Help Your Cat
Kidney disease can have horrible twists, turns, ups and downs. Many cats recover from what may at first seem like an insurmountable downswing. In Poopy's case, her first "crash" was her last. But some cats crash multiple times. I like to think she only crashed at the end because the medications and fluids I provided kept her from getting too bad off until the end was inevitable.
Much love and hugs....and chin scritches for the kitties.
