Ruby is a relatively young member of the Jupiter's Clan and is portrayed as having an aversion toward her family's killing of regular humans; several of Ruby's fingers are fused together, possibly from Syndactyly while the appearance of her face suggests Goldenhar syndrome.Ruby first appears in the film largely obscured from view at the Gas Haven where she takes a red hoodie from the Carter's car, which she wears throughout the rest of the film. When Bobby Carter accidentally knocks himself unconscious after finding the gutted remains of his dog Beauty, Ruby watches over him and hides him from Goggle, Beauty's killer.

When Lizard receives the order to kill the abducted Catherine Bukowski from Big Brain, Ruby overhears it and quickly flees with Catherine as Lizard advances on her with a meat cleaver. With Lizard chasing her, Ruby finds Catherine's father, Doug, and is about to give him Catherine when Lizard attacks him. Ducking away as Lizard beats Doug to the ground, Ruby remains helpless with Catherine as her homicidal brother advances on them. Before Lizard can attack Ruby or Catherine, Doug brutally attacks him, simultaneously beating him with a shotgun and shooting him with it. With Doug having incapacitated Lizard, Ruby gives him Catherine and, in an act of self sacrifice and freeing herself out of deformity, tackles Lizard, throwing them both off of a cliff when she sees him getting up, saving Doug and Catherine.