"Dancing, obviously," is her immediate response. She doesn't explicitly notice him standing straighter, but she does suddenly feel a little more conscious of their age difference--she skipped a few grades, so she's younger than him even though they're in the same year--and stubbornly tries to ignore it. It's not like they're here as anything but friends, and it doesn't matter anyway!

So she reaches out her hand to drag him over to dance. "Come on! They're playing some good music."