Growler, I am so sorry to hear about Duffy. Your words to me during Shade's illness and her death meant more to me than I can express. I wish I had some advice to give you about diets, but I can tell you that someone to look out for as well as increased DILUTED urination (caused by the kidneys inability to concentrate urine) is reduced urination which can indicate more severe renal failure and cause the buildup of nitrates in her body because of her kidneys inability to produce and excrete urine. I am somewhat familiar with kidney failure in people, but less so in animals.
I also looked at some of the websites that Rainbow posted, but found this tid bit... http://www.tarazet.com/mt/archives/002643.html
it says that this drug may help to improve appetite which can be a big issue for renal failure.
Keep her eating and drinking as much as possible, if she is diuresing (massive urination) she can become dehydrated and develop electrolyte imbalances and if she is not getting enough calories she will start to breakdown muscle which is protein.
Tell you vet that you are interested in information and ask them for resources including research studies. I am happy to help you understand the scientific stuff if you don't have a medical background. Please let me knwo if there is anything I can do to help you. All the best for you and Duffy