She doesn't see him go, but she knows when he's gone. Her plan was to check on him, try and get him to sleep--right up until she walks over to the bedroll she'd left him in and finds it empty. Then, her plan is to work a little longer and then go looking for him, but a whisper of cold air from the entrance makes her look up from where she's spreading a blanket over a sleeping, shivering patient.

He's back, and he looks a hell of a lot worse for his escape.

"Daryl!" He looks like he fell down out there, except even falling down, the snow wouldn't cling to him on all sides. Hurrying over to him, she holds out a hand, as if expecting him to start wobbling right then and there. "Jesus, what happened?"