I have some of the same questions as Shannon.
You do want to be feeding a good quality puppy food with a higher protein and, at that age, should probably be fed 4 times a day. Dies she look overweight?
Another question is has she been wormed and stools checked by a Vet? Better to get a good wormer from the Vet than those from a pet store.
What kind of food are you feeding her and how often? Puppies should be fed small meals every couple of hours throughout the day if they will do so. Make sure it is a name brand food and a PUPPY food (I personally LOVE the purina proplan diets). Another question, are her stools irregular? Do you notice undigested food, a shiny film to the feces?
It can be normal for puppies to always want food because they are growing. With her being a large breed dog, it is important for her to have high quality food, but to restrict her feeding to small, regular meals so that she doesn't grow too quickly and develop orthopedic problems.