That is "old school" thinking. A low protein diet just leads to muscle wasting and it's hard enough to keep weight on a CKD cat without losing muscle too. What's more important is that they eat a high quality protein.
Do you know what stage of CKD she's in?
What's more important for CKD is to feed a
low phosphorus food, and with the diabetes, you really need to keep working on getting her onto a low carb canned or raw food. Kibble is dehydrating, very hard on the kidneys and the most important thing to keep kidneys healthy is water!
The perfect food for a cat is a mouse which is about 80% water....just like canned food! Most of us even add extra water to the canned food to make our own "gravy" (which a lot of cats like).
If she's in late stage 2 or higher, you may need to add a phosphorus binder which keeps the phosphorus from breaking down into the bloodstream. It must be added to every meal, which again, is much easier with canned food.
Here's some
Tips on transitioning the hard core kibble addict .
Another thing that has been helpful is 1. to feed only on a schedule. Do not leave a bowl of kibble out all day. 2. at each feeding, put a teaspoon of wet food on a plate next to the kibble. Eventually, curiosity gets the best of most cats and they give it a try. It can take weeks (or months), but your cat will be healthier eating canned food, as nature intended. Whoever developed kibble in the first place didn't do our cats health any favors!
TANYA'S COMPREHENSIVE GUIDE TO FELINE CHRONIC KIDNEY DISEASE is the "Bible" for treating CKD but there is a LOT of information included. Don't let it overwhelm you and keep asking questions!