why is my dog throwing up when her puppys nurse?

She's doing what she should be doing. She is feeding the pups. Regurgitating is perfectly normal in fact, you state she throws up a little .. you will see that she will soon be regurgitating not small amounts but large amounts and the pups will all come running for dinner.

She is introducing them to soft solid foods ... You should have also started this 2 weeks ago starting with gruel. Which is dry kibble soaked with supplemental puppy formula or water and mashed until it is the consistency of a thinned oatmeal, then over the next several weeks you lessen the amount of liquid until they are eating dry kibble. You should also have fresh water available in a shallow bowl for them at all times.

She is not sick and does not need a visit to the vet. She is simply being a good mother. The pups will nurse for as long as the mother allows it.

LMAO @ Jenn and Lady . who obviously are not breeders

No its not stress its INSTINCT. If she didn't want them to nurse your dog is more than capable of getting that point across. Wild canine bitches do the same thing. Regurgitating predigested food is how pups are introduced to solid food. They want to nurse because their mother allows them to

I say call you local vet and see what they say. The would know best. Hope it gets better.