Looking at Eggshells or TCFeline Low Phosphorous

So, today I learned my kitten has renal agenesis(fancytalk for missing a kidney. She was my vet's first experience with it and he's been at it for twenty years, lucky me winning the jackpot). A simple spay turned into a 2 1/2 hour exploratory surgery with x-rays, and now I have one very uphappy, very stoned kitty with a very slightly enlarged kidney.

I want to switch her to a lower phosphorus diet, as right now she's on a premade 80/10/10 grind. What I'm wondering is A) how much eggshell does a cat generally eat per day and B) if I decide to use TCFeline, what is everyone's opinion of the ingredients therein? I haven't researched this sort of thing because well, who thinks their cat has a super rare birth defect.  I'm looking at the premix because she can be fussy and I have not tried a home-made diet yet because finding secreting organs has been a PITA, so this would be a possible backup if that falls through. Any input is greatly appreciated.

Here's the premix list of stuff

Ingredients:  whey protein isolate, calcium carbonate, taurine, freeze- dried krill, Xanthan gum (natural thickener),Vitamin B complex with Methylcobalamin (B12), Vitamin E, Vitamin D3, Vitamin A (Retinol)

Did your doctor advise to go with a low phos diet already...at such a young age?  I realize she only has one kidney, but couldn't feeding low phos result in possible OTHER health issues over the long run?   (I've had three kidney cats, so know about feeding low phos foods once they reach a certain state, but you aren't there yet )

mrsgreenjeens said:

 
Did your doctor advise to go with a low phos diet already...at such a young age?  I realize she only has one kidney, but couldn't feeding low phos result in possible OTHER health issues over the long run?   (I've had three kidney cats, so know about feeding low phos foods once they reach a certain state, but you aren't there yet

)

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What instructions have you gotten from your vet? 

If your cat really requires a low phosphorus diet just using a supplement pre-mix like TCFeline may not be enough. In a home made diet most of the phosphorus comes from the meat. 

None, aside from regular ultrasounds so far. I've had other raw feeders throwing the low phos at me, but the person who produces TCFeline advised changing nothing like you have said.  I would have updated sooner but I've been having a hell of a time getting sleep since I posted this, what with medicating and making sure she was getting enough fluids(admittedly I was in a bit of a panic when I asked, too).  Thanks for taking the time to reply.