This is truly shocking. I can only hope this is not happening in Germany, as I am a contractor for the Navy and work alongside wonderful service members and German Nationals.
In the German Army at least all guys were in the same shower at the same time no walls or anything.
No way a Janitor could sneak in and rape one of them. Didn't even have Janitors and cleaned our own mess. That probably kept everybody occupied all the time and if there is no freetime there is less chance of a guy raping anybody.
People even rumored that they had trouble in bed with their girlfriends since joining because the cooks put "hängolin" into the drinks. I guess it was just physical stress. But hey who knows and whatever makes them more harmless ☺
We had one guy in another platoon with different sexual orientation but he never did anything weird. Still some guys there made fun about not dropping the soap or even switched to shower gel so they don't have any soap to drop
20 men showering together with knives around their necks because one of them might possibly do something against one of 19 others would have been very surreal.
Today women are part of combat troops too and not just medical service. I can imagine that there aren't too many at times and might have to shower alone. If it were my sister I would sure she would carry something no matter how small the actual odds.
Good thing is in Germany there are almost no guns so a German janitor in an American base wouldn't have any. German soldiers also don't carry unless they are deployed or part of some guard platoon and what business would they possible have in an American Base? They wouldn't make it into the camp to begin with. So a German janitor forcing somebody would mean physical force or some less scary weapon like a knife.
Long story short you should be fine, especially from the locals. Maybe more likely that one of your own guys maybe superior in rank, capable of making your life hell and maybe even carrying a real handgun tries something funny. More opportunities and more means.