Hi Nicci,
Welcome to TDK land. We’re the fluffiest forum around. Thanks for rescuing the kits and I’m sorry the wee boy didn’t make it.
Kittens will eat as much as they need. KMR concentrate tends to give kits constipation and the liquid does the opposite. Here in TDKland, we recommend Goats’ milk for kittens. Cats are lactose intolerant and can’t digest cows milk. Goats’ milk is full of nutrients, probiotics and gentler on their tummies. This can also regulate the poop.
I’ve provided a weight chart for kittens. This an estimate and not written in stone. If she is eating, gaining weight, peeing/pooping then I don’t think it is a problem. She may take to a gruel rather than just milk so, you can make a gruel by mixing milk and wet food. When you do feed her the gruel, make sure you open up the nipple so she can suck it out.
FYI-you may put a soft blankie and something that smells like you (T-shirt) in her nest with a soft, stuffed toy. She will snuggle the toy and not be lonely.
Good Luck and I hope to see your wee girl as our TDK soon.
PG