She sounds perfect to me. When you get her home you will not be able to believe how small a 3lb puppy is, and a six pound adult to me is very small. My Shylah weighs seven pounds, and people cannot believe that she weighs that much.
The vet tech always weighs her about three times just to make sure because she looks so small. Brynna who is her littermate weighs nine pounds, and is according to my vet is the proper weight for her frame.
Tammy