"He was acting like he used to act." Maybe that should have tipped her off, but Shaun being an action-loving dumbass is normal for her. He's just usually careful underneath all the bluster.

She looks over at Clementine, curious in spite of herself. When she sees what Clementine is doing, she looks back down. Clementine is worried. It makes sense. She'd probably be worried about herself too.

"I'm not going to let myself die. I wouldn't--I can't let him come back to a world I'm not in."

He's already gotten to live in one of those. She won't put him through it again.