Hi Nicole, it’s good that you have taken this kitten to raise, as cow’s milk is not a good supplement for mother’s milk. The formula is okay, but what a lot of us like to use is goat’s milk. It’s easier on their tummies and has probiotics for their gut. You can find it in the refrigerated section where the milk is or in the baking aisle in cans. The canned is condensed, so add water 1 to 1. Everytime you switch a food, it usually shows in their poop. Not surprising, she has diarrhea, but also if you continue on the KMR, you more than likely will be dealing with constipation before too long. I found that KMR powdered causes it and the liquid KMR diarrhea. If you would feel better, you can always take her to another vet, you don’t want the diarrhea to continue very long as she will get dehydrated. A lot of vets don’t know a lot about hand rearing kittens, as most haven’t done it. I’m going to post some links for you, I’ve used them over and over while hand rearing. Good luck, and we are here if you need us if problems arise.
http://www.safehavenforcats.com/newborn.htm
http://messybeast.com/handrear.htm