You want to keep a whelping bitch fairly quiet and not too much exercise. You also won't want to let her out to run around unsupervised in case she starts having puppies outside.
The appropriate exercise for a whelping bitch is an exercise program which involves a daily run to make sure all of her muscles including her uterine muscle are in top condition.
Walking a dog is always an appropriate exercise. I'd start with that. Swimming is good too if she likes that sort of thing. =I would probably stick to those two.
You can allow her a simple and brief walk to use the restroom. She should not be running around hard or playing roughly while she is whelping. It is best to let her deliver her pups first then when she is finished give her a nice short brisk walk and not running at all.
Give her the freedom to run she will know exactly what her body needs but she has to be able to have the freedom to do it so she can keep herself heatlhy as well as the puppies and that will also make her labor and the birthing much easier on the female and the puppies.