The swollen arwea could be a simple sign that the pressure of the puppies put some stress on tat area and with rest and time it should clear up in a few times. If it does not take her to the vet as it could be a urinary track infection.
Yes this is normal that area has to be bigger. So that the puppy can be born. This is somewhat not a thing to be worried about. I would also consider to take the mother to the vet to get checked out. The swelling is normal after a few days it will go back to normal.