Can you get her to swallow food that you feed her by syringe?
Does she have diarrhea?
Try taking her temperature with a rectal thermometer. Normal is between 100 and 101.5. Higher than 102.5 is a fever and that will cause loss of appetite. If she has a fever and no other symptoms you can force feed her a few times a day to keep her blood sugar up and she will probably recover.
If Zoe isn't spayed yet (or even if she is), she is probably still producing milk, just much less than she was when she was nursing 5 kittens so it's not as noticeale. It's still important to get Kalley to eat other food, but there's no harm in letting her nurse because she's still probably getting milk and mom's milk is very good for sick babies.
A kitten who won't eat is an emergency and really needs to be seen by a vet, because the problems are often very treatable. Can you call your local humane society to see about low-cost options, or call local vets to see if you can apply for Care Credit?