Puppies really shouldn't be born more than an hour or so after one another. Pups are carried in the two horns of the uterus which is shaped like a Y. So sometimes there might be a little more time between the two sides. It is likely that the stillborn pup was stuck which caused its death. Other pups can be born after a stillbirth, but the longer it takes for them to be delivered, the higher the chance will be that they may not make it.
The following are things that indicate a vet visit should happen as it is a difficult delivery.
If your dog is actively straining to deliver a puppy for more than 20-25 minutes, or there is longer than an hour or so between puppies being born and you feel there are more puppies, she needs to be seen by a vet.
Sometimes puppies are too large to be born and get stuck. They can also experience uterine intertia and you need a visit to determine if a shot to restart labor is needed.
It isn't unusual for there to be from 10 minutes to an hour between puppies being born. So keep an eye on the clock and record the time each puppy is born so you can accurately judge when a vet visit may be needed.
Sometimes a female will not push in the house due to house training. Taking her outside with a towel to wrap the puppy in if it should be born can be attempted if you feel this is the case.
It is possible for a mother to not deliver all her pups. Usually when a pup is retained, a dog does not act normal. They may appear restless, distressed, actively straining, lethargic, non-interested in their pups.
However, if your dog is eating, drinking, urinating, nursing her puppies, cleaning them and basically acting normal, she has most likely delivered all her puppies.
If you feel there is a puppy still inside your female, then you should take her to the Vet to be sure. It's a good idea to take her and the pups in anyway for a post whelping checkup to ensure all placentas were delivered as well
Here is a site on this information.
I would have her seen as soon as possible if you still feel there are puppies left undelivered.
I hope you find this information helpful.