Do you know what stage of renal failure your cat is in?
This website is a fantastic resource for CKD/CRF cats, if you haven't seen it already.
Chronic Renal Failure is what they used to call Chronic Kidney Disease a few years ago, and it sounds scary but really depends on the stage. Regardless of stage, you want to feed canned food only, no dry. Getting as much moisture into your cat as possible is key. If your cat will tolerate mixing water in with the food, that's another good idea.
Next, it's important to choose a food that your cat will eat. Keeping their appetite up is very important. Sometimes, CKD kitties have a lot of acid in their stomach, and pepcid can help keep this under control. Talk to your vet about the dose if you think that this may be the case.
As far as types of food--unless your cat is in end stage renal failure, you want to go for a high quality protein, low phosphorus, low carb food. There's actually quite a few out there! Wellness has several pate flavors out there that fit the bill.
This food chart has a list of foods by phosphorus content. Try and stay under 250 mg/100 kcal of phosphorus, and under 10% carbs if you can. I would also stay away from foods with byproducts--stick to the premium brands that have higher quality ingredients.
If she is in end stage, you may want to talk to your vet about a prescription kidney diet (like Purina NF) if she'll eat it. It will be harder to keep her diabetes under control, but if the CKD is the larger concern you want to treat that with diet first and the diabetes second, adjusting her insulin to compensate. Sometimes those diets are appropriate for end stage CKD cats and sometimes they aren't--you'll have to discuss it with your vet based on her bloodwork and tests. I would not feed a prescription diet to an earlier stage cat--they cause muscle wasting and many cats don't like the taste for long.
