Who is Rebecca from Wasted: A Memoir of Anorexia and Bulimia and what is their importance?

Rebecca is one of the girls that befriends Marya at her new school in California. Rebecca tells Marya she found it hard to believe Marya was formerly anorexic as they ate Oreos in Rebecca's kitchen. When Marya returns home from Rebecca's house, she purges for the first time since she spent time in the eating disorders hospital. Later, when Marya's pants appear too big for her, Rebecca begins to openly show her concern about her friend's weight.