First of all, I am SO sorry for your loss
I know your heart is just broken
Secondly, did I read that right, did you get this puppy at 6 weeks of age?!?!
If so, that breeder is completely out of their mind, and THEY are to blame for the puppy not surviving. That is way too young to be away from Momma
Big hugs to you. I'd be beating that breeder's door down if she doesn't want to help you with the medical costs and/or replacing the puppy (with a 12 week old puppy, no younger than that).