I've never been offended online, but 90% of the time (if not more) when I play a game online I don't tell anyone my gender, nationality, sexuality, political orientation or what my favourite color is either. Since I don't have a mic, so no one can pick up on my gender when they hear my voice and I honestly don't see what me being girl has to do with me playing Modern Warfare, Company of Heroes or Left 4 Dead.
As far as I am concerned, I connect to play a game. I expect everyone else I play with to do the same. Last time I checked, the internet was a great place to be anonymous and it isn't required that I know anything about your or vice versa for us to play together.
I might be falling into the old rape-myth of "It is the victims fault", but I've always wondered just how girls that play games get singled out in the first place. With the advent of voip in games, I can see how it occasionally would be a problem, but this phenomena has been around longer than that. If you go out of your way to tell people what gender you are, aren't you actually highlighting the fact that you are different even if said difference has no impact on anything related to the game?