I recall different estimates showing from 8% up to 20% of wow population being females. However when you look at hardcore gamers, be it heavy pvp-ers or pve-ers, theorycrafters, achievement whores or speed levelers they will be ~99% male. And anyone who spends significant time preparing e.g. reading up on forums is also more likely to be male.
And my anecdotal evidence from playing for quite a few years indicates that women are playing wow more for social aspect and journey rather than destination. And fun fact is that all women players I knew that made it to hardcore raiding were excellent healers or tanks but I recall no dps.