"...sure," Zuko says, the hesitation only because she's surprised by Kitten's eagerness. "I'll probably train later today. I'll just have to see if Rin is interested."

Zuko doesn't really mind an audience, as long as that audience has some appreciation for what she's doing. The dragons here may not be firebenders exactly, and they may not understand it in the same way she does, but they still know fire. She's sure Kitten isn't about to call it 'jerkbending.'