Haibara is used to it. But more importantly, it means that the ruse is working. As long as people around her are convinced she's a normal child, she'll be safe from the suspicions of the organization out for her life.

"I'll be fine," she answers matter-of-factly. Then she kind of gestures back with her head to where people are probably still disembarking from the train. "Besides, I have a chaperone."

Masumi Sera had apparently volunteered to keep an eye on her. Not that Haibara needed it, of course.