I would imagine that if he was on the way to beat the crap out of his girlfriend, he was probably excreting some pretty intense body chemicals. My guess would be that she smelled that and knew something wasn't right. So, maybe not sixth sense, just really good fifth sense.I have never used schutzhund commands or directives to protect myself. Weird as it may sound, its my job to protect my dogs. That said, several years ago with my first GSD - not at all trained in protection sports, I learned that my dog Sita knew a threat and acted on it. I was living in an apartment at the time and walking Sita around the building to the back entrance at the end of an outing. It was dark outside and a man was standing there. I recognized him as the boyfriend of the gal who lived in the apartment above me. Sita had seen him before, but this time she growled and barked her head off as we got closer. I was taken aback at her reaction, but I just re-directed her and we went inside. About 10 minutes later I heard a loud noise and a scream from upstairs and a few minutes later six cop cars surrounded the apartment and I looked out the window and the police were taking this man away in handcuffs. He had beaten her while she was calling 911. Did Sita sense that this man was a threat? Same man at other times NEVER elicited this response, however I do believe that her GSD "sixth sense" somehow picked-up the fact that this man was up to no good at that moment.
I hope I am never faced with the situation that my dogs feel the need to protect me, but if the situation arises, I have faith that their instincts will prevail.