We were in the same boat, but tried “boot camp” and they said they couldn’t help her. Points for honesty I guess.
We’ve also had a rescue about three years. In some ways she’s very well trained, or she’s smart and cooperative. However she’d been a year at the shelter and been abandoned before that, so definitely not socialized. She has a scar on her snout that looks suspicious, and she reacted strongly against men. Basically I sat on the floor for two weeks tossing her treats before she would approach. Now she’s the most loving and protective dog to our family, she lets the cleaner in with a warning, is generally ok with people, and loves our neighbors. She is much improved.
However we were never able to stop her from pulling when on leash, never stop her from being dog reactive, and people better not surprise her.
The biggest thing she needs is that socialization, but reacts so strongly that no one is willing to risk their pet (nor I the liability). I hope it’s posturing since the couple times an off leash dog approached, it didn’t lead to anything, but she’s awfully aggressive with it