I'll share some of my experiences with my adorable, beloved Tuffy who was diagnosed at around 2 years old. (Aug 28 1996-July 17, 2004.)
Another member posted Helen's site that was started years ago because of her CRF/CKD kitty, Tanya. There is loads of information there, so I suggest you start there and read all you can about this disease and how to manage it. The link is: http://www.felinecrf.org/. This was one of the first sites I found when my Tuffy was diagnosed years ago. Helen has added a lot of information since then, so it is one of the first places I send folks to. Another site with helpful information and some supplements that have helped CKD kitties is: http://www.holisticat.com/crf.html.
With kitties with CKD, you do NOT want to limit their protein amount, as is still suggested by some vets, therefore they prescribe the nasty kidney food low in protein. Current advice in the last few years is to not limit protein, but limit phosphorus (see below). Do not feed a low protein diet, please. The reason you are seeing weight loss is because if kitties do not get enough protein from real meat in their diet, their bodies use their own muscle mass instead (simplified version of what happens). I mean, kitties are obligate (true) carnivores, and by restricting protein you are basically starving them. They need meat to survive, unlike humans and to some extent dogs.
What you do want to try to limit is the phosphorus amount in kitty food, but you can use a phosphorus binder mixed in every meal to help with that. (Helen's site has info on this.) I used Egg Shell Powder (ESP) as a phos binder for Tuffy per Holisticat's website. High phos levels in labs is one of the main causes for tummy upset and kitties generally feeling crappy and not eating. Keeping this under control can go a long way towards helping them feel better.
Kitties with CKD need to eat, so try to find foods with quality, real meat in the food, or whatever they will eat at other times. Canned is best, or even raw that maybe you lightly cook and then puree and add phos binder to it and a tiny amount of Egg Shell Powder (ESP) for a calcium source that won't raise her blood calcium levels. Chicken and turkey are lower phos meats. Egg whites that have been cooked (do NOT feed raw whites) are a good source of protein with lower phos, although some kitties aren't too fond of it--could maybe try cooking with some unsalted butter or other animal fat to make it more appetizing (this worked for my Tuffy). I would never feed a CKD kitty kibble unless that is all that they would eat.
Warming food slightly can bring out the aroma of foods when our little CKD kitties aren't too keen on eating. They also enjoy eating off your fingers. I found this such a bonding experience to do this with my Tuffy--it was one of the few positives we had in our life at that time. He also enjoyed drinking from a glass of water (I had one that had mL on the side so I could monitor how much he was drinking (see below).
Water, water, water! Next to a quality diet w/real meat (or as close as you can get), water is vitally important. It flushes toxins from the body that your now kidney impaired kitty needs to be done "manually" -- so to speak. I tried to give Tuffy sub-Q fluids, but he was quite the little fighter when it came to that, so I started adding extra water to his food, syringing by mouth 5-10mL, 4-5 or so times a day on the days he absolutely would not let me do sub-Q fluids. I aimed for 5-10mL per pound of his body weight. I kept a log of how much water I had added to his food and syringed throughout the day. I tested his hydration so that I knew if I needed to give more or not: lightly pinch some skin on the body, if it snaps right back down, they are hydrated. You can also feel their gums to see if they feel smooth or sticky--if sticky they need more water.
If you can do sub-Q fluids, get Terumo needles--they slide in like butter. Most vets give you crappy needles that are like pitch forks and hurt--at least my vet did back when Tuffy was to have sub-Q's. Maybe if I had known that beforehand, Tuffy might not have ended up hating it so much. <sigh> You want Lactated Ringers Solution (LRS) unless there is a darn good medical reason to go with a different type of sub-Q fluid. Some vets prescribe Normosol, but that can burn. Some others can raise their lab values, including urine pH.
Big ole hugs to you and your sweet little one. CKD can be managed, so just hang in there and learn all you can, but remember to take care of yourself too!