I was wondering how things are going with your foster dog. I've never fostered a dog that came from a true commercial puppy mill -- although I've had a few from what is considered by many to be a notoriously high volume breeder in TX. Although those dogs weren't caged 24/7 (at least to my understanding), there were definite signs of undersocialization and kind of a "free for all" as far as the dogs' interactions were concerned. (Lots of scars and missing fur on the face from fighting, a definite bite wound on one guy's leg, etc.)
For example, all three had issues with walking through doorways. I've had a few other people who have had dogs from this breeder mention this as an issue, so I can only guess that they weren't allowed in the house. That was easily fixed by leaving the door open and ignoring the skittishness about the doorway.
Basically, I think you'd want to expose the foster dog to a range of situations and things just like you would with a puppy. If it seems too stressful for her, don't force it, but come back to it another day after being successful with some other situation.
I would also encourage doing a lot of one-on-one training and bonding without the other dogs as "crutches" -- some modeling and social support is fine, but you don't want her to become so closely bonded to the pack that she freaks out when sent to a new home where she could possibly be an only dog.
Will she go back to the shelter or be adopted directly from your care? Regardless, I know she will benefit from her education in how to be a "normal dog" with you and your dogs.
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