Game developer Blizzard has already shown the male version of the Diablo III monk. It hasn't shown the female version. Until now.
Diablo III has four character classes announced so: Witch Doctor, Wizard, Barbarian, and Monk. This concept art is for the female version of the existing monk.
In previous games, players were locked to a class/sex combo.
The character's official page has the female in-game character model as well.
Check it out. And that pixie hair!