I also agree with increasing food. She may be going in there to feed the pups you just never see it. When my grandpa bred beagles he had the problem and set up a web cam and realized she went in to feed them but he never saw it. He also wondered how they were so fat but she never saw her feed them. Also we had an oops litter 2 years ago(mom wouldn't spay female). She would not let anyone but me and my mom by them. My brother and sister couldn't even go by them.