My thoughts on this, why not just get a nice, social, confident, high drivey dog and work him or her in a protection sport with reputable people.
Learn all you can and title the dog. IPO, ring, something with a good reputation and good people in the sport.
You like that dog, and she's got what it takes, go ahead after that and train her in some basic PPD work. It's not a huge leap from IPO to PPD with most dogs. Even prey can be channeled into some pretty serious "aggression".
I know next to nothing about GSD lines, except that I like what I see in some GSDs, when I see it. I am far more familiar with malinois pedigrees.
Where are you living that you see a need for a dog staying in the fight? All it takes is one look at my big male staring at them from a sit at my side, and next to nobody will bother me.
Many people have an almost primal fear of a big, strong, pointy-eared dog. Use that, and you won't need the dog to engage or stay in a fight, unless you are really in a bad area. And then-rock-paper-scissors... gun over dog.
Of course I am assuming you've got rock solid OB and a good human-dog relationship.