
I have to agree,taking a recently whelped bitch out for a walk is inviting germs back to the pups and infection to her very vulnerable uterus which will still have raw areas as they heal over.
I keep my newly whelped bitches upstairs in their own room which has a barrier across the door preventing her getting out and the others getting in, she can see and hear the comings and goings but feels safe and secure, after a week or so they want to be downstairs so Mum and pups move down into a closed crate which allows the others to see but not touch. By the time the pups are 4 weeks old the other dogs have been properly introduced to the pups and Mum is happy to share their care under supervision.
The problem I had was my bitch who had the pups was not in the position of top dog before the pups but wanted to be afterwards and the other bitch wasn't willing to give it up and fights would happen totally out of the blue so I had to be very careful that they were never left alone together, they would be paired with a male so they weren't isolated on their own.
You may have the same problem with your 2 bitches or all will return to normal when the pups are older and left for their new homes.
Keep us posted on how things go.