[ Okay, she can't hide the fact that "fake firebending" has got her intrigued, particularly coming from Sokka. In all the stories she's heard about him and their adventures the fact that he couldn't bend was sort of always a thing. Not a bad thing, just a THING. So she's still a little skeptical as she waits and watches and- ]

Woah! [ Amazement lights up her face as she actually leans closer to see the fire. ] Thats incredible! How are you doing that? [ For a moment she actually considers looking around to make sure Zuko or Wan weren't hiding and playing a joke on her, but it passes with only a few glances around the room. ] I can't believe it. And fake firebending too, not even fake waterbending!