Lina Leandersson - Let The Right One In

Leandersson applied for the role in Let the Right One In through a web-based casting service. After being contacted by child casting director Maggie Widstrand, she auditioned for the role three times before finally being cast. She was unaware that the role she was auditioning for was that of a vampire. "I was shocked", she later told Expressen; "I thought it was a more usual role." But as soon as she grew accustomed to the idea, "it became even more fun. I wanted to be a vampire when I was little", she said.

In the film, she plays Eli, a child vampire who develops a friendship with the main character, 12-year-old Oskar (played by Kåre Hedebrant). Oskar is frequently tormented by bullies. Eli initially tells Oskar to fight back, and rescues him in the end, killing three of the bullies in process. Because Eli is supposed to be an androgynous character in the film, director Tomas Alfredson decided to overdub Leandersson's voice with a less feminine one. "Lina's voice is beautiful, but I thought it was too high in pitch", he said. Eli's voice throughout the whole film was provided by Elif Ceylan. In an interview with Dagens Nyheter, Leandersson laughingly commented that "it was actually nice to be dubbed, my voice sounds weird".

Leandersson and Hedebrant were never allowed to read the script. Instead, the director would read their lines aloud to them before every scene. According to Leandersson, "Tomas is a good teller. I listened very carefully." She identified the most difficult parts as the ones where she was supposed to be angry, and the transitioning between being normal and "crazy". In an interview, Leandersson recalled how she went totally into her role, to the point of "becoming" the character Eli, but affirmed that there are few similarities between herself and her character, describing Eli as more mature and contemplative. While she found it uncomfortable to film outdoor scenes in temperatures down to −30°C, she described her experience as "the most fun has ever had."

When asked about the biggest challenge in making the film, Alfredson mentioned the fact that people already would have a perception of the characters and the surroundings from the novel. He especially felt that the depiction of Eli was difficult, but stated that he was "very happy about Lina". On another occasion, he again commented positively on Leandersson's appearance, stating that "e hardly used makeup or anything in post-production to make her like this, she is simply damn good. She's also a very special girl, which I think shows in the film." He has frequently commended Leandersson for her intelligence, often comparing her to "an 80-year-old woman, very wise and very quiet."