Creative Director of Assassin's Creed Unity, Alex Amancio said a female assassin character was originally planned, but was dropped due to resource constraints:
It's double the animations, it's double the voices, all that stuff and double the visual assets, especially because we have customizable assassins. It was really a lot of extra production work.
The animation director of Assassin's Creed 3, Jonathan Cooper responded to this statement on Twitter saying it would only a day or two of work, not the 8000 animations Amancio has claimed.
Head to 21:37 to hear what Amancio has to say for yourself. What do you think, is "more work" a reason to not have a female character? Do you care about gender representation in games?