We can't tell who she is, and it's unlikely that she's playable. But it nevertheless looks like Assassin's Creed: Unity, like earlier games in the series, will have female assassins. No comment from Ubisoft.
The lady appears briefly at around the 7:24 mark of a new making-of video posted today by gaming site IGN.
Unity, which takes place in Revolutionary France, was criticised by some journalists and fans during E3 for not including the option to play as female assassins despite the inclusion of customisation options and co-op play. One of the criticisms was that, simply, the most famous assassin from the real French Revolution was a woman, so an absence of female assassins would be weird. Ubisoft promised to show female characters prior to the game's October release. This must be our first glimpse.