You have to race her to the vet. The vet can't get it out either. It gets stuck. Mom tries to help it out by clamping her teeth over one of the back legs. The head and shoulders are firmly caught.
Mom pulls on the leg, hard, peeling the flesh from the leg and leaving a wiggling stump of bone.
A dead puppy gets stuck in the birth canal, but your female is well into hard labor. The mother has no idea what to do with a puppy and she drops them out and walks away, leaving them in the sack to drown. The mother takes one look at the puppies, decides they are disgusting droppings and tries to smother them in anything she can find to bury them in. The mother gets too enthusiastic in her removal of the placenta and umbilical cord, and rips the cord out leaving a gushing hole pulsing blood all over you as you try in vain to stop the bleeding. Or, she pulls on the cords so hard she disembowels the puppies as they are born and you have a box full of tiny, kicking babies with a tangle of guts the size of a walnut hanging from their stomachs.