The relationship between Laurel Mercer and Emma Becker. Since Emma took Sutton's place she has grown closer to Laurel when Sutton pushed her away.
Once Emma comes and be's Sutton she and Laurel bond and grow closer.
Laurel Mercer: "Why would you change in the middle of the night? Okay, Sutton, this isn't funny anymore. It's like you're intentionally trying to make me think there's two of you."
Emma: "There are two of us. Laurel, I'm Emma, Sutton's twin sister, and...I'm gonna need your help."