|Wonder Woman||Egg Fu|
|Any Avenger Villain|
|Any X-men Villain|
|Power Girl||No one special|
|Black Canary||Lady Shiva|
|Batgirl||James Gordon, Jr.|
|She Hulk||No one special|
Reviewing the list of possible heroes who could have their own films, I wanted to see what the best options were for female leads. So I came up with the above list. I tried to avoid heroes who were simply defined by their male counterpart, unless the character is well know outside comic fandom. So, that removed Hawkgirl, Mary Marvel, Big Barda, Ms. Martian, Mera, Arrowette, etc. Also, I removed any lesser versions of a character, Dr. Light, the alternate Batgirls, the female Captain Marvel, etc. And I removed female characters who are mainly defined by their group; Legion of Superheroes, X-Men, Birds of Prey, Blackhawk, Asgardians.
Reviewing the above candidates shows the major problem, a lack of easily identified villains. This has always been the problem for Wonder Woman. Only two of the above have villains who are specific to them alone, Wonder Woman and Batwoman. However look at Wonder Woman's villains; Egg Fu and Ares. With one you have an extreme racial stereotype who has the major advantage of tying up Wonder Woman with his mustache. The other assumes the audience understands Ares is not a Dodge vehicle, but the Greek version of Mars, the God of War.
Most of list really depends on villains from other heroes. Black Canary and Batgirl have Batman villains, though I did list those who have a stronger connection to B.C and Barbara Gordon (Batgirl) than Batman. These both could make good films, but DC has been killing off the best villains like the Joker. So unless they start playing for the long run, they will quickly run out of the best villains. The Wasp uses villains from the Avengers and largely from Captain America. Depending on how they introduce her in Ant-Man, she might make a stand alone film.
Storm and Rogue could an excellent choice for a team up in a film. Both are X-Men and both have been seen before by audiences. Halley Berry as Storm is one of her better performances and could easily get backing for a female lead film. But the choice of villain is important. You can't use Magneto, he has been reformed. You can't use Mystique, Rogue's personal foe and stepmother, she is not evil enough. Perhaps introducing Apocalypse might be a start and that way you could have Rogue become the first of the Horsemen of the Apocalypse.
Black Widow would seem to be a natural, except two of her best villains were killed in The Wolverine, Silver Samurai and Viper. That leaves just Snapdragon. Knowing how studios love multiple bad guys so they can make more toys, it seems unlikely.
I like She Hulk, but that would be a really tough sell. She is a female version of the Hulk who is also a lawyer. With that description, all I can here is Tom Hanks in Big when he looks at the robot that turns into a building. "I don't get it."
That pretty much leaves us with Batwoman. I can already hear the bitching and moaning about having a gay superhero as the lead, but really she is the best fit. Batwoman has a couple of iconic villains, Alice and Bloody Mary. She stands on her own and an original film would not be as tedious for fans as another retelling of Batman or Superman. She can draw from the Gotham menagerie as well. She has a lot to recommend her and it could become the Brokeback Mountain of superhero films.