Rachel feels like her annoying, self-indulgent younger sister, Amy (recurring guest star Christina Applegate, who won an Emmy Award for her previous "Friends" guest appearance), is finally on the verge of making a major change in her attitude. In order to help Amy become a more responsible person, Rachel overrides Ross' strong protests and allows Amy to baby-sit Emma. She soon regrets that decision. Meanwhile, Phoebe unknowingly thwarts Mike's (recurring guest star Paul Rudd) "anniversary" surprise for her. Also, Monica and Chandler become concerned when Joey tries to use big words in a recommendation letter on their behalf to a child adoption agency.