
I would contact the manufacturer if it doesn't cover pregnancy in the notes on the packaging (unfortunately my last lot is all in Dutch).
If at all possible I would just keep grooming her, and treat the house (with her out of it) with acclaim, as most fleas will be in the environment.
Avoid using anything until pups are born. Once they are a few days old you can treat her, and keep her away from the pups until the coat is fully dry.