Actually, I think that's a very fortuitous situation and I'd take her back frequently to play if you can
We take puppies from their new homes at around the 8-10 week mark, because that's an ideal time for them to bond with their new families. But in doing so, we interrupt their learning on a number of important life issues - how to be a dog, bite inhibition, social orders, discipline, etc And we have to compensate that by doing some of the teaching ourselves, and by finding as many socialisation opportunities (eg. puppy kindergarten classes) as we can to give them the opportunity to socialise with others their own age.
It sounds as though you've the opportunity to have the best of both worlds here. Your pup is settling in well with you (and you note she isn't pining), but you've got ready socialisation experiences for her with her littermates pretty much on tap. As long as you include a range of other socialisation experiences for her also, I'd say you should end up with a well rounded puppy out of that