I am so sorry you are going through this - and also poor little Bella. Such a hard start to life.
Depending on the laws in your state, it might not matter whether or not the breeder is taking responsibility. Selling a dog that young may be illegal in your state and the breeder may be able to be reported to animal control to be cited for this, and small claims court might be an option in the future to get some of these medical bills paid if your vet is willing to state the dog was sold w the coccidia present at the time of sale - also depending on what the laws in your state are.
I would start thinking of going to another vet. She is just so tiny and young. Maybe you could start a thread to see if there is anyone in your area who knows of a reputable vet who is AAHA accredited. I found this one
http://www.google.com/url?sa=t&rct=j...I6tWlhbe7J7nRQ
but I have no exp in your area of the country w vets.
I am sure you are close to emotional and physical exhaustion. Hopefully a vet can help her through this and help you know if there are any laws or resources in your neck of the woods to help you. You are in our prayers. Please feel free to PM me if you need someone to talk to.
Just a thought, Carmen knows other breeders who are mentors. Perhaps she knows of a vet in your area or knows someone who does.