The biggest issue with the renal prescription foods is that they are still made based on the old idea that less protein is better for CKD cats. Cats, as they age, need more protein, not less, to help compensate for muscle mass loss that is very common among older cats. - CKD or not. There is a section about this on Tanya's web site, take another look at it specifically.
I have also heard that a lot of cats just don't like the prescription foods, or if they initially eat it they get tired of it very quickly. Maybe split her food between this food and others that have more protein? Personally speaking, you'd be better off feeding Zoe good canned food and when her phosphorus numbers increase to the point that matches the guidelines on Tanya's web site, ask your vet about a phosphorus binder. Tanya's Comprehensive Guide to Feline Chronic Kidney Disease - Diet and Nutrition Overview (felinecrf.org). This section also includes a list of foods with lower phosphorus that you might be able to consider.
I have also heard that a lot of cats just don't like the prescription foods, or if they initially eat it they get tired of it very quickly. Maybe split her food between this food and others that have more protein? Personally speaking, you'd be better off feeding Zoe good canned food and when her phosphorus numbers increase to the point that matches the guidelines on Tanya's web site, ask your vet about a phosphorus binder. Tanya's Comprehensive Guide to Feline Chronic Kidney Disease - Diet and Nutrition Overview (felinecrf.org). This section also includes a list of foods with lower phosphorus that you might be able to consider.