Greta (Lola Kirke) is a hidden villainess of the 2014 film Gone Girl, as well as Gillian Flynn's 2012 novel of the same title. She is the girlfriend of Jeff, and was introduced meeting new motel guest Amy Dunne (the hidden main villainess of both the novel and its film adaptation), who had gone into hiding after framing her husband Nick for her own "murder."
Amy was able to befriend Greta by acting as though she used to be in an abusive relationship, as Greta was also revealed to have had an abusive ex-lover in the past. Amy later watched coverage of the case against Nick with Greta, becoming offended by Greta's lack of sympathy for Amy due to believing her to be "uppity" and having brought her "death" on herself by marrying Nick.
Later on, while playing mini-golf with Greta and Jeff, Amy accidentally dropped the waist purse she was using to hold her money, with the two lovers taking notice of the large amount of money she had. With that in mind, they later went to Amy's room and began searching said room for her money, eventually finding it under her mattress. As Jeff taunted Amy, she asked Greta if he'd convinced her to help rob her, only for Greta to reveal that she had convinced Jeff to do so. When Amy threatened to call the police, Greta revealed that she'd been taking notice of Amy's odd behavior and realized that she was hiding something; therefore, she wouldn't call the police on them. Greta then said she didn't believe Amy had ever been abused before having Jeff throw her onto her bed as she marvelled at the money in Amy's purse. The villainous couple then left, with Greta warning Amy to be careful next time, claiming there were "a lot of people out there a lot worse than them."