Our new baby boy weighs 10.4lbs at 8 wks. I was a little concerned because he was pretty skinny in comparasion to the Boxer pups I've seen at this age. We consulted our vet (who ruled out any parasites) & then explained that puppies of all breeds tend to be somewhat skinnier out here because of the heat (Nevada). We're used to fatter puppies from Kentucky, where it's not well over 100 degrees everyday.
When concerned about your pup, always consult your vet first, but we all have to consider parentage, climate, etc, etc, etc.
Good luck with your new little girl!