And pretty much from the moment you meet her, it’s fairly clear that there’s more to her than her lighthearted, bubbleheaded persona, long before she uses her battle skills. Look at what happens when Azula recruits her.
Azula used blatant intimidation tactics to get Ty Lee to comply, ordering the net to be set on fire and all the animals released (which, for the record, would not only have endangered Ty Lee but the circus creatures themselves–I bet Ty Lee was attached to them, and that would’ve been a double threat in itself). Ty Lee is visibly terrified, but instead of calling her out or letting Azula see that she was intimidated, she says this:
Instead of endangering herself by pointing out that Azula crossed a line, Ty Lee falls back on her talk of “the universe” and “auras,” talk that canonically gets her indulged or dismissed but never taken seriously.
She knows that Azula’s dangerous. There’s no way she doesn’t know that Azula is threatening her. But if she can keep Azula from realizing she knows that, she’s a little safer.
Because she’s one of maybe two people Azula never considered as potential enemies–even (especially, but that’s another thread) Ozai is a threat in her mind, but Mai and Ty Lee are the closest thing Azula has to trusted friends, right up until their betrayal.
Ty Lee’s spent a lifetime cultivating a personality that not only allows her to stands out among her siblings–it protects her from being treated as a threat. When you’re friends with Azula, that is an essential facade to maintain. and she does it consistently enough that no one ever sees through it.
All of the Fire Nation kids are so messed up. Zuko’s just the one who gets in the most trouble, because he’s the only one who doesn’t have a mask.