It can be a couple things, Lack of food or water and they will, yes if they die off they will eat them, if they don't have enough fat or protein in diet. Also if you have mothers fighting over babies accidents happen and then they will eat the dead babies. All things to check. And yes some people say first time mothers will do that and some will disagree. I wouldn't write her off just this instant unless you have plenty of mothers to replace her with.