Amy Green is Rachel's younger sister. Amy comes to Rachel twice, both times because of boyfriend problems. She repeatedly calls Emma, Rachel and Ross's daughter, wrongly. She first thought Emma was a boy called Emmett. The next time she appears she keeps calling Emma "Ella". The first time she sees the baby, she declares "You know what would be great? If you guys died!", thinking she would inherit the baby and her trials and tribulations would be made into a movie (similar to Baby Boom with Diane Keaton). She is, however, greatly offended when she learns that actually Chandler and Monica would get custody of the baby Emma instead. She and Rachel then started fighting when Amy said that Emma was not cute. Chandler sorted them out like a father would do.
Having later become engaged to the wealthy father of an old boyfriend, she is convinced by Rachel to leave Myron - her fiancee - and try to make a new life on her own, only for this attempt to fall apart when she has Emma's ears pierced while babysitting her. Rachel and Ross flip out and Rachel forces Amy to move out, Amy claiming that she has decided to become a "baby stylist", giving fashion advice for infants. Before Amy leaves, Rachel and Amy make up by gossiping about their sister Jill, who has gotten fat.
During her appearances Amy is depicted as being a very unpleasant, abrasive, amoral and utterly unlikable person. She displayed a great lack of tact, a poor memory (initially failing to recognize Ross and Monica and subsequently insulting them while describing them) and bossiness, ordering Joey around even though in Season 10 she calls him his roommate. She thought that Phoebe was Emma and that when she told her real name, Amy thought it was a noise. It is implied that she also steals jewelry; on her first visit, when Rachel learns that Amy is at the door she immediately pleads with Ross "Hide my rings!"
Amy also reveals that she used to make out with Barry during the time that he and Rachel were together.
Amy is also one of the few women that Joey can't stand, much like he can't stand Janice. At one point, he tells Ross "She may be the hottest girl I've ever hated."
- She was shown to have interest in sushi by mentioning it twice in two episodes.
- In The One With Rachel's Sister, Phoebe mentions that Amy once bit Rachel, whilst Jill is the spoiled one.
- Although she was a deliberately unpleasant and unlikable character, much like her father Leonard, the comic relief she provided caused her to, also like her father, become memorable as a character fans "loved to hate".
- Both of her appearances as Amy earned Christina Applegate nominations for a Primetime Emmy Award for Outstanding Guest Actress in a Comedy Series, winning the first.