rejection of litter

Question
My dog had its litter 5 days ago now and she had 4 pups 2 boy and 2 girls we have been hand rearing them because she was rejecting them on the day of their birth, she was ok with the first 2 pups but after the 3rd she started getting funny, by this i mean licking and cleaning them like a normal bitch would and then bitting them gently
but when they squeek she bites harder. We tried this about 6 times she was doing the same every time cleaning then biting. We rang the vets to ask about this and they said give her a days rest for a day.. So we gave her a rest and tried her again but when she came back in the room she cleaned it and then grabbed it with a chomp like she was trying to kill it this made it bleed .. Since this we have taken her away from the pups as we are worried about their saftey but when she hears them cry she whines as if she is worried also she has been bringing a certain toy to us and picking it up gentley as if to show use something ..... i am wondering is it possible she can go back with the pups ? or will she try to kill them again

Answer
How old is your female?  If she's a young female sometimes it takes awhile for the mothering hormones to kick in.  But then, there are just some females that were never meant to be mothers.

I would stay with her the entire time and put the pups with her for short periods of time only.  Instead of all 4, I would rotate them 2 at a time, they could be overwhelming her.

Good luck.