Sorry to hear you are dealing with that dual diagnosis, but it's something I had to deal with as well. One resource for diabetic friendly CKD files is listed in this file:
CKD food Chart
With Neko it was a lot of experimenting with various low phosphorus foods to see which ones she liked. When she was first diagnosed with CKD, she would still eat her usual foods, but with the dual small cell lymphoma and heart disease conditions tacked onto her resume, I had to start the hunt for alternatives. Due to changes in her mouth due to acromegaly, I also had to add water and purree it into a mousse like texture. Sometimes I even had to syringe feed a bit of food first, to prime her stomach. She'd usually eat more on her own once she got the first few bites in. I even used some of the Royal Canin Recovery, which is low carb and easy to syringe. And better yet, Neko liked the taste.
I have used the transdermal maropitant (Cerenia) in a current kitty and do find it works for her. I haven't seen diarrhea resulting. I'm giving it for vomiting and support for pancreatitis episodes. For actual nausea, I like ondansetron better. You have to give it more frequently, but it works way better. If you have a hard time pilling, there is an injectable version, though I've heard it can sting.
Neko made me up my pilling game. She was part Maine Coon, big and strong! I ended up with a pilling gun that really helped. I stuffed as many meds as a I could into a blank gel cap, and used that to pill her. She was getting nausea meds as well as other oral meds for heart disease, lymphoma, and supplements for CKD.
If the Mirataz - presuming that is what you have - is making her a crazy eater, try giving a lower amount. With Mirataz that is easy to do as it is also transdermal, just measure out a smaller amount. I find I don't have to give it every day, maybe every few days.