Online poker's so often such an ego-driven testosterone-fest, I think it's definitely +EV for other players to think you're a female--a lot of guy will play you differently than they would if they thought you were a man. If I were to come up with a new Party nickname, I would (seriously) use something like:

SoccerMom
NatesGrandma (cause who wants to stack a grandma?)
Noobgirl
InnocentGirlWhosNeverPlayedPokerBeforeISwear

You get the point...