Never watched the cartoon but the movie is really, really bad. The only good thing in it is Dev Patel. It's a shame that they ruined a perfectly good idea. But yeah, it has a lot of similarities with your main plot - a world where people can control elements (only one element, and not all of the people can do that), and there is a prophecy about the one who shall be able to control all of the elements.. But he'll have to be one of the Airbenders... So the bad guys kill all of the Airbenders, just in case, but one kid accidentally survives, and of course, he is that last Airbender who now needs to learn how to control his power over the other elements... And to reclaim his right to rule, and save the world from the bad guys.
Just to clarify, I wasn't trying to suggest you explicitly make it about feminism as much as taking taking advantage of obvious gender differences to distinguish your story from traditional fare. For example, the movie "Elizabeth" with Cate Blanchett can be looked upon as simply a coming of age story. But through the eyes of a female it takes a new life as she fends of suitors and maintain legitimacy among her male advisors. It's not feminist. But rather she faces different challenges and requires different solutions than what a male would in similar circumstances. That's a little different than say changing Frodo's name to Frida but giving her the same challenges on the road to Mordor. I'll stop there as it's your story. I just wanted to highlight some opportunities you have to differentiate your story. I suspect you are already there - just wanted to offer encouragement. Good luck!
Oh, no, I didn't mean to imply that you implied that I make it about feminism, if that makes any sense... lol I just wanted to clarify that it wasn't a novel based around feminism. I knew what you meant. And I appreciate the advice. It's definitely making me rethink some things to make it more of a struggle for her.