She's making it impossible to stop smiling. It's just as well he's nowhere near his workplace or people would stop seeing him as the scarily stern head warden. The comment is all well and good, but seeing her actually hit the target makes him proud.

"There you go! Good job!" He might be a touch excited as he does a few more corrections. "You're shorter than a lot of the people coming here, so you have to aim higher than you'd expect. It might feel wrong, but you'll get results, trust me."