While I cannot say for any certainty that this would be "normal" (only your vet can tell you for certain), oftentimes, the queening nest is very warm with all those little ones whose body temperature is 100+ degrees piling on top of Mom, who is also 100+ degrees. I know my own queen did breathe a little harder when she was in the nest with her babies. However, she did not pant, as such.
One of my favorite things to say in situations like this is: If you ~think~ something is wrong, it probably is. And if you think it is wrong, then the best advice you can get is from your vet.