Hi Robert,
Welcome back! First, I'm so sorry to hear about Jemma.
Dr. Hodgkins' book is a great resource, and I agree that the "prescription" diets aren't good. Cats are obligate carnivores and need meat, and that doesn't change because of kidney failure. So a good-quality, grain-free canned food, or even raw if you're comfortable, with the phosphorus binder would be good. Raw or wet food has a lot of moisture in it, which would help her hydration in general, and not put as much stress on her kidneys compared to dry. Chopped, cooked egg white can also bind phosphorus.
In my "The Veternarian's Guide to Natural Remedies for Cats" (which is from 1999, so some of the information is out-dated), one vet mentions Renatrate by Progressive Laboratories, 1/2 tablet twice a day. The company still exists:
https://simplynutrients.com/Renatrate-p1200.htmlHe also recommends 3-5 drops of Renal Drops by Professional Health Products, which is a "combination homeopathic remedy to help rebuild kidneys":
https://professional-health-products.com/product/renal/ You may want to contact them to find out what's in it, since the page doesn't list ingredients.
Dr. Hovfe states in the book that it's best to feed wet food and what the cat likes. She recommends a home-prepared diet and a supplement called Renafood by Standard Process, 1-2 tablets a day, crushed and added to food. I checked and this company is also still in business:
https://www.standardprocess.com/products/renafoodFinally, I checked Dr. Hovfe's site, Little Big Cat, and found this article on kidney disease:
https://littlebigcat.com/kidney-disease-in-older-cats/If you have time, I would research those supplements and see if you feel comfortable with them, but hopefully this gives you a place to start.
Sending purrs to you and Jemma!
P.S. I just looked at Dr. Pitcairn's book, he does mention reducing protein, with which I don't agree (the book is from 2005). He does mention giving good quality protein and states "it is vital to replace water-soluble vitamins that get flushed out of the body easily, especially vitamins B and C, and to supply plenty of vitamin A, which is good for the kidneys."
More from Dr. Pitcairn: "Many cats with kidney disease will develop a state of low potassium levels in the body, which further complicates the situation and creates symptoms in its own right. If your cat does not respond adequately to the treatments suggested here (and below), consult your veterinarian about adding a potassium gluconate supplement to this diet."
Be advised that his diets are home-cooked and include rice, and if your cat isn't used to home-cooked, she may not eat it. Dr. Pitcairn lists some herbal and homeopathic remedies as well.