We are fighting this same battle with our Lucy. I thought at first that she was a finicky eater, but it turns out that she gets nauseous from time to time. We tried Hills and Royal Canin. Lucy would not eat either of them (so now I cook for her). I do remember reading from others that their pups liked the Purina (like Sammy's Mom said). It's a tough, uphill battle though. I included a link to nutritional data of some of the brands out there. I'm sorry it's a long read, but I was hoping it would help you decide what to try next. Hugs to you and Zoey.
DogAware.com Health: Prescription Diets for Dogs with Kidney Disease