Marcy Miller is a girl that attends James Woods Regional High School.
When Chris Griffin is attracted to her in "An App a Day", he takes Neil Goldman's advice to send her a picture of his penis from his cell phone. When her father finds it later, he complains to the school and Chris is labeled as a sex offender and forced to attend a rehabilitation class.
But when he finds he is still treated as a pariah, he steps up his actions and has himself chemically castrated. No longer obsessed with masturbation, he improves his grades and is able to tutor students. But when he impresses Marcy, her flirting with him undoes the chemicals, returning Chris to normal.