Well, if she's doing a lot of vomiting and can't keep anything down, then maybe I would take her. But right now she's not eating. I would have thought that maybe throwing up the big hairball would help her to feel better. I only asked about the vomiting in case she was doing a lot of it -- you wouldn't want her to get dehydrated. It doesn't sound like you are at the stage where she gets sub-q fluids at home since she's in early stage renal disease. If I have a cat that's vomiting a lot, I will give Cerenia, but I'm lucky to have a stockpile of it at home. Of course, if the problem persists beyond a day or so, or if other things are involved that are concerning, I would take kitty to the vet. It sounds like your main problem now is getting her to eat. Can she have any of the old food for the time being (like in a separate room like a bathroom?) Just to get her to eat something? Or did you get rid of all of it? And then try again slowly to mix the old and new foods? OBTW, I've been feeding a lot of the Weruva BFF PLAY foods that are low in carbs and in phosphorus. They are pates and there are quite a few flavors. I don't know if you've tried them. Have you seen this list? Click on the Diabetic CKD Foods List and you will see a lot of food options (sorry this is not helpful in the short term, but just another bunch of food options and information.)
https://www.bizave.com/foodlists/Combined_Food_Lists_Feeding_Guide.pdf