Mark Chance
Boingy! Boingy!
It is important to remember that few players actually ever see what we'd be able to call a statistically relevant sample of GMs. What you're actually going to see is apt to be more dependent upon the social circle(s) in question than how many female gamers there are in general.
Well noted. I've played with female GMs, but not in recent years since my gaming group is deliberately a Man's Day sort of thing.