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Just a word of advice from someone who's gone through this in the past and
is going through it now:  If it gets to the point where your kitty is really
disinterested in food and has lost a lot of weight, if you can find
something she likes (even if it's not so kidney friendly), try to go for it.
Since you say the renal disease is very advanced, you may eventually find
that you need to focus on keeping your kitty from losing more weight rather
than worrying about additional damage to her kidneys.  For the last year of
Molly's life, she lost a lot of weight, and the only thing she would eat was
human tuna, which is not the least bit kidney-friendly and lacks taurine and
other nutrients required by cats. I supplemented her with feline vitamins.
She lived for nearly a year on this regimen. At the very end, she was
willing to eat small amounts of shredded steak and nothing else, so I
provided that for her. Good luck. My heart goes out to you.
Best regards,
---Cindy S.