
I have a toy breed known for their birthing difficulties. Until I bred my self whelping line I genuinely lost count of how many sections I have had. I have never been prescribed painkillers - with a breed that can be quite wimpy. My experience has been that however much pain a bitch is in, she will stoically ignore her own discomfort while she gives her all to her whelps.
However, I once had an extremely sensitive bitch who was absolutely demented with pain (she had shown little to no interest in her pups.) I went to the vet hospital determined that I would get her help. The vet I saw said that she couldn't have anything, as her pups would be affected. I insisted that I be given the pain relief. He did stress over and over and over that she couldn't feed her pups. He obviously didn't know me well enough to know if I knew what I was doing.
Well, no pup can ever be as important as my bitches, so I crated my bitch and covered her crate. Doped up to the eyeballs she eventually destressed bless her. I tried to hand rear, and had the pups PTS eventually as they just did not thrive and looked worse than runts. They would have died eventually anyway as they were losing weight every day. When you start with 2oz pups it isn't easy.
But that was just my experience. As your bitch is feeding her pups remember that she will be in pain anyway. Pups suckling will encourage the uterus to contract. I don't think your bitch would be feeding if she couldn't stand the pain at all.