I would agree that female GSD's are more aggressive than males. I've had bad encounters with GSD's, about the only breed I have a real problem with (I love Pits), and all of them were female. One thing about female dogs in general, the fights they have are way more serious than most fights between males.
The two biggest GSD's I've ever seen were females, the biggest one was a neighbor's dog that was just immense. A mid 60's import from Eastern Europe "Zonia", she scared the hell out of a lot of people just from the way she would stare at you. She liked me a lot, and would come see me daily on her patrol of the neighborhood. If my friends were with me, most of them were just terrified of her, and her growling and locking eyes when she wanted a chin rub didn't help. She was at least 125 pounds. The Lab that lived next door to her was 100 pounds, and he was much easier to pick up than Zonia was.
The second biggest one, "Greta" was just a really nice dog, a few pounds lighter than Zonia, with less hair, but a whole different attitude than Zonia had. Greta and a neighbor's female Doberman got into a huge fight with the Dobe ending up in the hospital overnight. Greta had already fought with the same neighbor's male Dobe, and she just let him go when he decided to cut and run, but with the female, she was deadly serious.