
It's like C sections, there can be a good non hereditary reason for one, so breeding again would be OK after a lot of thought if essential, if it ahppenes again, then I would question the adviseability of breeding from that bitch, I would keep a bitch pup and mate her very carefuly to a line that had good history of easy whelping.
I agree there never should have been a third litter let alone a fourth, the risk to the bitch and pups is just not worth it, as well as perhaps fixing breeding difficulties into a line.