I would try to seperate them when they are about to give birth. Realize they are animals and even the smallest thing can throw there routine into chaos. My first breeder rat ever had a nice litter of 13 when i first got her the next was about the same but she ate all but like 5. The only thing left were males and at that time i was extremely female heavy on my rat ratio so think that was her way of giving more males the chance to survive but none of the females. Introduced a couple more males into my growing rat collection and this last litter was 16 and has been the ideal mother since. So feeding her off is definately an option but not necessarily the only answer. I would give her one more chance by herself in a maturnity tub before i would give up on her.