The first two weeks we keep the pups in a small carrier with warming pads to keep the pups warm and only take them out every two hours when it is feeding time. Once they are over two weeks old we move them to a whelping pin so mom can get to them, but we still keep a close eye on them, so mom won't accidentally lay on one. We never let her alone with them for very long, if so we will put them in a small crate, until they are bigger, by then they are almost weened and they can stay with mom all the time. I would keep a close eye on her and the pups in a secure room that she can not get out of (baby gate), she only gets out when you let her out. That pup might have something wrong with it that she can sense. I don't know were you live, but I'm assuming it is cold outside, so I hope the pup didn't get too cold, because it could die from getting too cold. Good luck and keep an eye on those precious pups and don't rely on mom to totally take care of them.