That's very cool. But for the most part, I think it's fine the way it is now. The only SMALL addition I would is maybe two small line around where her stomach is to give the waist a bit more definition. One small line that shows where her ribs end, and another small one going down the stomach to give it a more muscular definition.

She looks plain without her Sais. That drawing is pretty kick ass. If not he sais, then some finger nails or something... and make the mask a little see-through or something.