Both my labs came to me from breeders who recommended ProPlan puppy chicken and rice- just regular, not large breed. They both said the pups could be upgraded to adult food at about 4 months of age- some say wait until their adult teeth are in, some breeders recommend they stay on puppy food much longer. I switched to adult food at about 5 months of age but stayed with ProPlan so that they were getting pretty much the same vitamin/mineral mix and other ingredients. Labs are not considered large breed dogs, however, I think they're kind of on the border of medium and large based on their adult weight. I think either would be OK. If she's on Purina puppy chow, you could probably go to ProPlan now without much disruption to her system.
Mine were getting about 3/4 cup of food 3 times per day at 9 weeks which went up to one cup 3 times a day by 12 weeks. My girl stayed at about that amount and now that she's full grown gets 1 cup, twice a day. My boy was up to more like 4 cups a day by 4 months of age. I switched from 3 meals a day to 2 meals a day at about 6 months of age- same amount of food total, just divided into 2 meals rather than 3. After he finished growing, I backed down and now, at 8 years of age, he's getting a heaping cup twice a day. You'll have to judge the amount by how they're looking/feeling.