Wow, can I relate. I haven't read all the posts, except for the last few, including the bit about returning the dog to the trainer...
Our oldest dog Gracie had horrifying dog aggression. Walks were a nightmare of constantly looking for signs that other dogs might be around, crossing streets to avoid oncoming dogs, constant, constant anxiety. No one could bring a dog over to the house. There were maybe 2 or 3 dogs that she was "friends" with (would tolerate) but that was it. Otherwise, encounters became fights. She drew blood on three occasions (twice when people brought their dogs over unannounced to our house and once with one of her "friends"). It was horrible, horrible. The last straw was about 3 years ago, when she spotted a neighbour's dog way down the road, and charged it. They were understanding (their dog was loose too) but it was rattling.
So we did some research and found a trainer. One speciaized in working dogs and dogs with aggression. We bit the $ bullet and did private lessons for 4 months. We each worked with her twice a day. We walked the crap out of her. We worked with many dogs, with the trainer, in class. The first dog-dog encounter was probably exactly like what you saw during Thorn's assessment...awful. The thing was, by the end of the second class, our trainer had Gracie walking on-leash, BETWEEN the trainer and another dog (one who she'd tried to kill earlier) whose leash was being held in the same hand as hers. We knew we were on to something at that point. A prong collar became the tool we used to compliment all the work/training we put in, and it is a tool I highly recommend for "hard" dogs (not all dogs, but some).
The result...just to show you there CAN be light at the end of the tunnel:
- we were able to take Gracie to a dog park
- I can go jogging or walking with her, on leash, past homes with furiously barking dogs, and she trots by without so much as a glance
- the neighbour's dogs can come over without fear of getting hurt
- she is a calmer, happier, more relaxed dog
- we now are a three
-dog home, and a harmonious one at that
...a note on this...while introducing Jaida to the pack was initially a delicate matter, it proved to be absolutely INVALUABLE to Gracie in terms of her learning polite dog behaviour and how to interact with her own kind...from Jaida she learned patience, how to walk away, and how to communicate without biting. It got even better with the addition of the third dog...Heidi taught Gracie how to play (how to initiate it and respond to invitations, and how to enjoy it). I strongly beleive that constant or extremely frequent time spent with a sound, well-socialized, polite dog is one of the best possible tools for working with dog aggression...
so on that note, if your breeder is willing to help with this, and can help your dog with controlled routine exposure to/interaction with other dogs...I'd be inclined to give it a try...