I had a mom try to eat her newborn once. Luckily I had another mom with milk and I put the little boy with her. She was spayed and placed in a pet home and is doing well, some of them just aren't cut out to be moms I guess.
I have a friend also who had a similar thing happen, except they were 8 week old pups. Her unspayed female (not their mom) jumped the xpen and killed one of the 8 week olds. She had her spayed and placed her.