Lynn Shelton Offers a Thank-You to Sundance PARK CITY, Utah - For the films screening here, the crew from "Your Sister's Sister" might have been the most relaxed. Not only did the film already have distribution, a rarity at this year's buyer-ready festival, but it came with a lot of good buzz from its premiere at the Toronto International Film Festival in September. That's where IFC picked up the film, a largely improvised comedy about a depressed guy (Mark Duplass), his best friend (Emily Blunt) and her sister (Rosemarie DeWitt), with plans to release it this summer. So the movie, directed by a Sundance favorite, Lynn Shelton ("Humpday"), was not in competition here. But Ms. Shelton nonetheless felt it was important to show it. "I feel like I owe Sundance so much," she said at the after-party on Friday night. "We had such a Cinderella experience here with "Humpday,"" which won a special jury prize in 2009. Without that stamp of approval, she added, "I don't think that Emily and Rose would've come to me and wanted to work - I wouldn't have been able to seduce them to work on such a tiny project." Not that it was easy to get "Your Sister's Sister" made. Though Ms. Shelton and Ms. Blunt spent months on the phone, talking about the back story for the characters, Ms. DeWitt came on board late, after another actress dropped out, and had to work around her schedule for "United States of Tara," the Showtime series that has since been canceled. She was flown back and forth between that set and the Washington State island location for "Your Sister's Sister." With a skeleton crew, the movie was shot in just 12 days. "I was terrified we weren't going to get everything completed," Ms. Shelton said. She had just finished directing an episode of "Mad Men," which has a production schedule of eight days per episode. With only the framework of a script, she was extra dependent on her actors to deliver. But she had an experienced improviser in Mr. Duplass, who starred in "Humpday" and brought the idea for "Your Sister's Sister" to Ms. Shelton. He also produced. With his brother Jay, he's an improvisational filmmaker in his own right ("Cyrus"), but credited Ms. Blunt with upping his game as an actor. "She taught me how to do movie star" stuff, he said, using a less polished word. "I know how to be glib and loose and natural, but she can do that" and give the right look to the camera, he said, calling it an ability to be simultaneously unself-conscious in her character and self-consciously aware that she's modeling. "She gets chemistry out of every guy she's with," he added. But Ms. Blunt took issue with the idea that she gave him any movie star secrets. "I told him to comb his hair tonight," she said. But there were never any moments where I said, this is when we do our Blue Steel for the camera. Correction: Jan. 21, 2012 An earlier version of this post misstated the title of Lynn Shelton's new film. It is "Your Sister's Sister," not "My Sister's Sister."