Take a gander at the Big Sister:
According to one report, the Big Sisters are "amazonian version(s) of the Big Daddy, wearing similar, though svelter, gear" and that they will be "faster and sleeker" than Big Daddies.
So if you're a fan of the BioShock mythos, you're probably wondering as much as I am right now: where do Big Sisters come from? We already know the story of the Big Daddies and the original Little Sisters. Nowhere in the original BioShock was it ever hinted that there might be a female version of the Big Daddy.
I wonder if there's a Big Momma somewhere in Rapture...