How does Jodi Picoult use imagery in Mercy?

Imagery:

"The moon sat cross-legged on the windowsill, its white skirt reaching to the plush bedroom carpet. It turned Allie into a creature of light, someone she would not recognize in a mirror; someone who was as sure of her worth as she was of her beauty."

"Then she straightened imperceptibly, just enough for the muscles and the marrow in her bones to realize she had taken the first step toward separation."