I personally think that from the current lot of characters and considering the storyline, the only female that has a chance of winning the tournament is Asuka. Will that happen? Most unlikely, but let me point out some things:
1. Nina is revered as the strongest female character (at least among tekken fans), but she will never win the tournament. Don't take this as prejudice, but this is a Japanese video game and probably the typical anime/manga stereotypes hold for its story. The sexy leathal blond mature female character that plays a secondary/independent role is not important enough to win the tournament. The teenage cute/tomboyish Japanese school girl type>>>>>> the mature sexy lady type in anime/manga. Japanese teenagers are the strongest thing in the universe in anime/manga!
2. Asuka has the Kazama bloodline that nullifies the powers of the devil gene. None of the other females has anything that even comes close to that. Whether Asuka could defeat a base Mishima or not is irrelevant. She nullifies their strongest weapon. Not even Nina stands a chance against a Mishima with his devil powers unleashed.
3. She has the closest thing of a tie to the Mishimas. None of the others is important/close enough to win the tournament.
4. Sure her story is crap right now with her stupid lili rivalry, but this doesn't mean that namco cannot give her a more serious relevant story in the future tekken. For all we know, she could be the central character in the next tekken (lol who am I kidding?! It'll be Larsy-boy).
Realistically, Nina should have the best chance of being the first female iron fist champion, and based on her profession and extensive experience, she should be able to slaughter any of the females without even trying. However, she's not a Japanese teenage girl with a special bloodline (or GIGANTIC hands!