Is it safe to use air conditioning for my dog and her new puppies?

Puppies are prone to getting cold, so I would only do this if it seems that it's too hot in their environment. You can start with a low amount of AC if needed and turn it up if they tolerate it well. You will know the puppies are too cold if they forming a tight huddle next to or under mom. If they are more spread out, then this would indicate that they are very warm.

I hope that helps and all is well with the pups.