okay, a little back story. Mom cat was a stray who was picked up had two very small kittens that passed. The shelter had kittens brought in around the same age as her kittens 1-2 days old. Mom cat is nursing the kittens. She refuses to use the litter box. She has not used the restroom in about 12-24 hours. I reached out to my rescue is this normal? I don't think she has been cleaning kittens. She will only feed them in a crate that is hidden. HELP