I try to stay out of these, but...
Let's see. Inconsistent, center of her own universe, overgenerous in judging her own character and undergenerous to others (especially authority figures), and often moved by impulse over principle? Or, as you put it:
Basically, she's perfect and everything she does is right and everyone else is stupid and everything they do is wrong.
Mr. Tweedy, you have just described every young person I have ever known. And most of the older people. Perhaps you were never such a person, and perhaps most of the people you associate with don't display these traits -- and if that's the case, kudos. Or is it more that you
do see these traits in people all the time, and that's why it annoys you to see them in fiction?
Whatever your reasons for finding Nahautu an active irritant in the story, they're fine and valid. We all have different buttons that set us off, particularly when it comes to personalities. (E.g., I've been watching Battlestar Galactica over Skype with
Minx, and she
hates Mrs. Tigh with a passion that really surprised me. She has deep personal issues with manipulative women, and that character brings them all out. She actually cheered when... Oh wait, no spoilers.)
I have a different view. I consider the variability and slight unreliability of Ms. Jemisin's protagonist a strength. I don't think this story would have worked as well with a Heinleinian superwoman; nor with a weaker homebody who did only what everyone expected of her. This is a character in unstable balance, with conflicting tensions -- and I find that interesting and believable. If she bought entirely into the spacemens' vision, we wouldn't feel the same impact over the passing of the Earth. If she was
entirely bought into her tribes' culture and never felt the urge to wander -- then she'd probably be married and out of her father's house by this point, and who would tell the story? This was the right character, in the right place, at the right time.
That doesn't mean you have to like her. But from a dramatic perspective, I think the author succeeded at what she was trying to do.