Females that have just given birth NEED lots of food! Doesn't matter whether it is one puppy or 6, they need to feed that puppy. Good for you for feeding her puppy food---it has more calories per cup than regular kibble. All dogs do go 'off' their food for a few days before giving birth.
I had an Irish Setter YEARS ago who gave birth to 11 puppies, 9 survived. She was ravenous. My mom had a full loaf of bread out, turned around and that dog had it. She brought to her pups, but then ate most of it. Pups had to put up with crumbs!