Anil is correct, every litter size can very. My doberman has produced as little as 6 pups and as many as 10. I've heard of some doberman producing 14!
How long was her labour? Was she straining a lot? How is her bleeding? What size were the puppies? (usually the bigger they are, the less there are)
She could have a puppy stuck in the birth canal, so it's necessary to examine her by a vet if you feel that may be the case.