I have dealt with some pretty messed up dogs, and IMO, it is very rare for a dog to be too emotionally damaged to recover.
In cases like yours, where the dog is otherwise great and emotionally healthy, there is always hope.
That kind of aggression is usually based in fear and insecurity combined with poor early socialization, but it can be overcome
Anecdote that may make you feel better: My wonderful boy Kojak was a total wreck when I got him. Severe long term mange, heartworms, and major abuse. For the first four months, he would do nothing but sit and the end of the hall and stare at the corner. SO and I would be in the living room, watching TV and playing with my other dogs, and he would just sit alone and stare at the wall.
One day he bounded into the room holding a toy and dropped it in front of Artie (another dog)! I burst into tears, actually...
It was a long slow road, but today he is a completely different dog. Playful, outgoing and wonderful. Being part of a family and being around emotionally whole dogs (along with a lot of training) pulled him out of it. He still has scars, he's quite shy around new people and he'll wreck the house if he's alone, but he's a new pooch today.
Of course his response was less outwardly dangerous so it's a different thing. He turned inward and shut down, it sounds like your girl is being rather...proactive.
But don't lose hope, dogs are resilient and can heal from things that would destroy people. It sounds like you hit the jackpot with Jamie