[gemy]

Oh how heartbreaking!!. I certainly hope the last pup makes it. There are many details missing from you post, such as, did the other female show aggression before the litter, was this the "first time" of aggression, or also was this the first time the female was allowed into the room with the litter of pups?

Irrespective the attacker female should Never be breed. Wrong and faulty temperament.

Obviously if your Mom elects to keep both females, and she breeds the other again, total separation of females until the pups go to their homes.