How does Misty Bernall use imagery in She Said Yes: The Unlikely Martyrdom of Cassie Bernall?

Imagery:

"When she left she had still been this gloomy, head-down, say-nothing girl. But that day—the day she came back—she was bouncy and excited about what had happened to her."

"Doctors say that brain forgets pain, and that may be so. I am not sure the heart forgets."