When I first started gaming the idea of a girl gamer was like the idea of a unicorn-- rare and unbelievable. But the truth is there are more females that game now than ever before (someone mentioned a statistic of 40% female player base in current gaming culture). So it is no longer the 'OMG freakin' UNICORN!!', it is a part of the culture as a whole. Yeah, so many people still treat girl gamers as rare but the truth is, if there are 40%, 4 of every 10 players you may encounter is conceivably of actual female persuasion.
Look at it this way: my generation grew up playing games and we had children. We also shared our love of gaming with our children. Many of us have had female children so we increased the pool of female gamers just because we decided to procreate and the toss of the dice gave us girl-children to share our love of gaming with.
Now these girl-children are adult gamers who will most likely go on to have children (girls and boys-- although statistically more will have female children) that they will share their love of gaming with (if they haven't had their own children already). If people still insist on treating the idea of 'girl gamers' as rare and unbelievable that is their own hang-up because the truth is females play games. More now than ever before.
In my own home there is a 3 to 1 ration of female gamers to male gamers. Not so rare anymore, are they?