How suggestive is your game? Will the 'rape' part leave a lasting impression? With mature content it is ALWAYS best to leave things up to the player to decipher what you are saying. Don't openly say "She is being raped." But say something like, "Some men did some unspeakable things to her which made her the way she is." That way it's more open to interpretation than just out and offending someone.
I'll generally agree, but I wouldn't say "always". I can think of one adventure mod for Neverwinter Nights that pretty graphically depicts a rape, but that scene was vital to the story. If it hadn't been done that way, the story would have suffered tremendously for it. It was an 18+ mod for nudity and some other content, but even if they kept it from 18+ land, that scene would have to stay in the mod to tell the story the author wanted to tell.
I can think of a few movies I could say the same for, as well as movies that used rape scenes that really could've done without them (rape just for "shock value" and a bit of gratituous nudity). So it can work both ways.
Back to the OP question: in the US, guns and blood and killing people in general easily fall in the bottom end of the 'Teen' rating (if there was a rating between 'Teen' and 'Everyone' it would probably go there. That's Saturday morning cartoon stuff. I can remember my girlfriend waking up with nightmares after watching the episode of the 'new' Johnny Quest where a woman gets eaten by fish things...
Rape would probably still fall in teen as long as the woman's shirt stays on. Nipples automatically go into 'M' ('R' if it's a movie), unless it's breastfeeding or "indigenous peoples", and even there you have to be careful.
Germany has all sorts of weird laws - people all have to have green blood in them, and you can only kill them certain ways, and a bunch of other stuff that makes no sense to me but I'm sure to Germans it makes perfect sense. Then again, Germany has laws that make it a crime to walk down the street certain ways (cue: Monty Python skit).