I think part of the reason some people don't speak up is that they don't want to get accused of "white-knighting" a girl. A lot of times on the net when a guy sticks up for a girl, people will look at him and say, "you're just defending her because you want to impress her and you want her to like you," even if he's just trying to do the right thing.
We shouldn't worry about that kind of bullshit. If some random dumbass pubbie is treating any player (boy or girl) like crap, call them on it. Let them know, "hey, that's not cool, and it's against server rules. Knock it off." Unfortunately, sometimes admins aren't around and can't mute/kick/ban the d-bags, but sometimes if the majority of the players speak up, you can make it clear that that kind of crap is not okay, and maybe they'll stop or say sorry or just leave. We also have votekick commands and stuff, so don't be hesitant to use those against abusive players.
EDIT: Oh also, sometimes when I play TF2 I get really into it and I don't really pay that much attention to the text chat, so I'll miss stuff that's said there. If someone says something to you that you find seriously find offensive (racism, sexism, etc.) while I'm there playing and I don't do anything about it, feel free to MSG me on Steam and say "hey that guy said something pretty terrible." I don't mind stopping to take care of it. This doesn't apply to just the women in the community either, it goes for all of our pleasant players who are credit-to-community.