What a beautiful puppy!! Congratulations on your new family member! How old is she? I got my puppy when he was 7 weeks, our vet put him on a special diet and told us to feed him more meals because she wanted him to be around 7 or 8 pounds based on his size at that time. He had one litter mate that was twice his size and weight at 7 weeks, every dog is different. I think if you're worried about her size you should bring her to the vet. They'll examine her and make sure she is perfectly healthy and if they feel she needs diet changes or any other special care they should have plenty of advice. You'll need bring her to one anyways for vaccines, so at least it's not extra.

Also not to worry you, especially if she isn't showing symptoms but, puppies are prone to parasites. Our guy was underweight when we got him because he had a parasite that caused him to throw up and have diarrhea. He was treated, put on a special prescription diet and within 1 day there was noticeable differences. In 4 days he went from 5 pounds and 4 ounces to 9 pounds and our vet was thrilled with his weight being there at 8 weeks. Now he is on his normal kibble and a very healthy puppy. I just feel like anytime there is a concern it is best to bring your dog to a vet to actually be seen. As helpful as the people one this site are and trust me there are so many amazing people here and THEY ARE EXTREMELY HELPFUL!! Hands on care from a vet is where you get the real answers.