Have you checked her teats? In any case, at 4.5 weeks weaning should be well underway with the puppies having 4 meals of solids a day, and only being topped up by mum. As this progresses, you should be able to just let her into the box to clean up after the puppies have finished at which point they will suckle, with her standing up until their sharp teeth start to cause pain and she wants OUT.
She could be producing more milk than they are taking off now too - in which case she might have mastitis - so do check the teats.
Try having her off them more than in with them.
For future reference, pregnant/nursing mothers do NOT need 'puppy food'. That's for .... guess what ..... puppies! She should have been on her normal good quality food, from mating, through pregnancy, to whelping and nursing. Perhaps with some added food like scrambled egg, extra meat if she has a big litter.
Are her stools normal? Could she simply be too hot around the puppies? Stressed - which can cause panting.
Obviously the best and only answer is to talk to her vet. We can really only guess what's going on. I have to say even if she came into season before you could get her spayed (it happens) if she was caught when you didn't keep a watch on her, she should have had a gravid spay.