Sarcasm is an adjusted stress reaction.

I feel like she'd have to be trusted with something huge. Like, actually tasked with running a city, or a military unit, or something. But I can't imagine a circumstance in which she'd be allowed to. ... Well, if Zuko died, I could see Mai thinking it was a good idea, actually, but I would feel bad about fridging Zuko and his little face.

Alternately it could all be c/o Iroh, who I think in a big way (even though he is my favorite) is responsible for the fact that she never had anyone who thought she was valuable but Ozai, and is already well-trained in the assisted redemption/maturation of cranky teens.