You poor thing. GSD pups are truly bad sometimes.
If your pup is getting correct amount of excersise and mental stimulation, then it sounds more like she is getting over tired, over stimulated and bratty. Keep a leash on her. If she is coming at you with that intensity and single minded ness, give her a time out. Take the leash, say nothing, and place her in her crate. Then walk away. I suspect she will holler for a bit then fall asleep.
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