There are three stages to labor. The first is before pups are born, then the second is when the pups are born and the last stage if after the pups are born and the uterus is still contracting to help push out the fluids from birth. So panting after delivery for a day or two is due to those uterine contractions. In addition, when pups nurse from their mother, the uterine contracts as well which is another way that nature helps clean out the uterus after delivery. These contractions cause a female to pant more than she would normally. The puppy nails can also lead to some discomfort and more panting. I dont' think her heavy breathing is an issue at this point but you will want to monitor her for a few other post labor conditions.
If your dog has a Green, smelly discharge from her vulva, fever, loss of appetite and listlessness, it is possible she has a uterine infection due to bacteria or a retained placenta and needs to be seen immediately. It is likely she has metritis which is a uterine infection.
If your dog is experiences muscle weakness, muscle spasms, tremors or seizures, limb paralyses, she needs to be seen now as it is possible she has eclampsia. Calcium supplements, Tums, cottage cheese or goat’s milk may help, but it might not reverse the symptoms quickly enough.
Here is a site with more information on this.
Look for breast infections on a regular basis Keeping the pup's nails clipped will help prevent this. If a breast becomes inflamed, red and hard to the touch, your dog will need to be seen by your vet.
It is possible she was aggressive toward the pups due to the pain of birth or that the pups were born dead or that she chewed the cord too close and kept right on going when she tasted the blood and intestines. It does happen which is why many breeders take the pup as soon as it is born, break the sac, cut the cord, clear the airway and dry the pup themselves before giving it back to the mom to nurse.
If this was her first litter then she will likely do a lot better with the next litter. If with the next litter you also have a large number of pups that can not be revived you might not want to repeat this particular breeding.
I hope I've given you great service. If so, I'd appreciate a 5 star rating. The rating should be based on my answer and not any site issue. Experts are not compensated until a rating is done. If you have any other questions at all, please reply here and I'll be happy to follow up with you even after you have rated. .