Quinn has been Samara's friend since second grade. She seems to have a very comfortable relationship with Samara.
Samara tells Emily that she is supposed to meet up with a friend the night of Emily's fashion show, so Emily invites Samara to come and bring her friend, without having met this friend. When Samara shows up with Quinn at the fashion show, the two share a joke about sitting in each other's lap, and Emily catches a touchy-feely vibe from the two. When questioned about it by Emily later, Samara claims that Quinn is only a close friend.
Quinn comes over to Hanna's House for the poker party, along with Zoey, Bianca, and Samara. As the girls leave at the end of their friends' night out, Quinn sees Emily give their friend Zoey her number, leading her to believe that Emily is trying to start another relationship behind Samara's back. She tells Samara, which makes her upset and angry. It is speculated that Quinn is jealous of Samara's budding relationship with Emily and used any excuse to drive a wedge between them.
Season 2 (2/25)
Samara [about playing house with Quinn]: I was the Mrs. and she was always the mister.