The only female character of any consequence that is not part of one of the families and yet is still interesting would be Zatanna. The magic angle definately works. If the proposed JL: Dark ever gets made, she would certaonly be worth having a standalone movie.
As for the others...aside from the fact that we a not likely to get a superhero movie with a female lead for a while...but the pickins are slim
Supergirl...derrivative of Superman...he would have to get a SERIES of movies before she would even get one
Batgirl...derrivative of Batman...Batman, Robin and probably Nightwing are more likely to get a movie first.
Batwoman...even less likely than Batgirl.
Catwoman...this could work, but only AFTER another Batman reboot.
Mary Marvel...not a chance in hell. Mary is much less interesting that Billy. She is not really a stand alone character anyway.