Heavy panting

my dog has puppies 3 weeks old and every time she lays down to nurse she pants heavily heavily heavily her nostrils flare out her flaps of her gums flare out and her she has white gums

Hello! - this sounds as though this could, at worst, be life-threatening; white gums and panting suggest an emergency.  We would highly recommend that she is triaged by a vet as soon as possible to try and rule out some of the more concerning possibilities but they might well want to see her immediately.