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Are you able to post a picture? it may be that she is passing the placentas. There should a placenta for each puppy. Do you know how many puppies she was expecting? X-rays of her before giving birth an tell us how many puppies to expect. If that number did not match the number of puppies she actually had then there are puppies left inside. If she is not done having puppies, then she may need help to ave the rest or she may need more time. If you do not know how many puppies she had then i recommend a trip to the vet for X-rays to see if there are any more puppies left in her.
There can be quite some time between puppies but not usually more than 1-2 hours.