
This is why at this age I bring the pups to the area that we are in most, as the maternal ties and those to us and the rest of their canine pack start to vie.
This encourages the bitch to stay with the pups, though I would not expect most to stay in the whelping box with them if they can see and hear them.
As long as she goes in with them at least every couple of hours, and as you say they are content and gaining then perfectly normal.
I have only had the odd bitch who wanted to spend her time with the pups when not actively caring for them, and these were the ones who liked being curled up in a bed with a chum anyway.
The majority of mine prefer to stretch out somewhere cooler.