Awww, it is sad and I think I know how you feel. It would have been nice to help the poor dog, but she may have been ill with something that she could have passed on to Chewy and you don't want that.
Poor baby, sounds like she either hasn't been handled much or has been mistreated
Do you know if this person has a lot of dogs? She could possibly be a puppy miller or a broker.
I think you probably made the right decision. This little gal could have cost you hundreds and hundreds in vet bills and a broken heart.
I'm sorry it didn't work out better. My heart goes out to you and the little doggy.