Mary gets a few points for a sensible approach to the matter! Even though she's getting some key assumptions wrong.

Trowa nods slightly, but says, calmly, "I'm not exhausted."

"It's important to assess performance levels accurately and without assumptions. I'd be asleep if I needed to be."

Not with a civilian twelve-year-old on solo watch in hostile territory, he wouldn't be, or at least not so deeply he wouldn't wake at small noises. But Mary doesn't need to know that part.