
As you only mention one pup, and didn't mention being worried about the others, I suspect that this pup was born with it's insides hanging out, and she just cleaned it all up. The pup would have died anyway.
If she is showing good maternal behaviour to the others I doubt she caused the pups death.
If you breed from her again take special note of her behaviour toward the newborn pups, and stay with her until they are all born, from start to finish.
Another reason, usually some time after pups are born, that can cuse a bitch to kill her pups, is Eclampsia, where the bitch's body becomes depleted of Calcium. this can cause the bitch's death,a nd a special liquid Calcium has to be given throughout lactation.