One for Sorrow

I think it fits with her not caring, which the show seems to hit pretty hard. It's not just that she doesn't care enough to make a stand against Azula in that moment, it's that she doesn't care about anyone or anything. So she doesn't care about the fate of her brother. If she has a moment of fear or caring when Azula first surprises her (I'd have to watch the scene again to see if they gave her any sort of moment like that) she immediately lets it go. Either way it's "whatever" to Mai. She's kind of dead inside.