The most common reason for this in pups is intestinal parasites such as worms, coccidia, giardia etc. A fresh stool sample checked by your vet can tell you if that is the problem.
If she is going outside and eating frozen stools the frozen stuff in her stomach can make her vomit.
However as she is a puppy she could have swallowed a non food item which is causing a blockage and could make her vomit smell like feces due to the blockage.
If the vet sees no parasites in the stool you might want to have her checked out.
And the easiest way to keep her from eating the stool is to clean it up and throw it away before she can do it.
Hope this helps you!
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