Links to read about rehabbing a mill pup:
Please note that they all stress patience and letting the pup set the pace. Otherwise, you can do more damage and things go backward instead of forward.
Adopting a puppy mill dog can be challenging but rewarding Working with Puppy Mill Dogs Caring for a Rescued Puppy Mill Breeding Dog speakingforspot.com
A quote from the above link that is true: -
Enter the process with realistic expectations. Understand that your rescued dog may not ever be a “normal” pet in terms of her trainability and responses to new people, other animals, places, and things.