In 2007, she had a role in the comedy drama "Lars and the Real Girl" as Karin, the supportive sister-in-law of Ryan Gosling's title character. The film received generally positive reviews; Deborah Ross of "The Spectator" thought Mortimer played her character well despite the film's repetitive comedic moments. Next in 2008, Mortimer starred opposite Ryan Reynolds in the comedy "Chaos Theory". Critical reception was mostly mixed, and Ruthe Stein of "San Francisco Chronicle" thought Mortimer and Reynolds lacked chemistry. The psychological thriller "Transsiberian" (2008), directed by Brad Anderson, saw Mortimer cast as Jessie. She co-stars with Woody Harrelson, and they portray a couple who befriend a pair of mysterious travellers. The film premiered at the 2008 Sundance Film Festival to a positive response; "Variety" magazine's critic thought Mortimer's character was well-developed, and it was "a very flavorful performance as a reformed bad girl".