Welcome to BPO! Awwwww. Little bit is so cuteee! What a cute name too!! hehehe I bet that was a great surprise on christmas!!! Sounds like she will fit in your family perfectly.
As far as the food goes, puppy food is ok as long as it is formulated for large/giant breeds. I've had Miles on tons of different foods already. All life stages, giant breed puppy, another all life stages, another giant breed puppy, and finally now, an adult food (but can also be used as all life stages.) Miles has never really done good on any of these foods. The food he's on now is still new to him (California Natural Herring and Sweet Potato), but he is doing best on it so far. I would recommend to go with what your pets do best on. I agree Pedigree and Purina aren't the best foods out there as they have alot of fillers and somewhat "unknown" ingredients in them, but if your dogs do well on it, I don't see a problem feeding it. Just my opinion.
By the way, I'm Samantha, mom to a 6 month old great pyrenees, Miles. I remember when miles was 8 weeks and that small. It seems like just yesterday! Now, he's 75 pounds of fluff!