That included dressing British actor Daniel Craig, who plays the lead role of investigative journalist Mikael Blomkvist and may be best known for playing James Bond.
"He was also one of my favorites," Summerville said. "He just looks great in clothing, and it was nice to kind of give him this sweater-y, soft, wrinkled look that he's, you know, you're not used to seeing him in because he's so immaculate in Bond."
When it comes to making characters look authentic, Summerville said, she is into "aging" their clothes. There's a whole science to the process -- washing leather jackets to make them look more worn, wadding or tying up pieces, sanding them, even using bleach and a mixture of lemon juice and orange juice so the acid breaks down the fabrics. But the unusual magic touch is beans.
"The girls in Sweden thought that was the funniest thing," Summerville said. "They had never seen that before, where I would sew stockings with beans and then you put them, like heavy beans, and you put them in all the pockets of the quilting so that it gives it that slouchy [look], like you had your hands in your pocket, or that you've owned something for quite a long time."
She brought her aging techniques to H&M to incorporate the look into the mass-produced line. When she first presented the collection, Summerville said seeing H&M division designer Anna Norling and creative director Donald Schneider's faces light up was a great moment. But what sealed the deal for her was when she showed it to director Fincher and Mara.
"David was like, 'It's really f---ing good,' it was just kind of like the seal of approval," Summerville said, "especially coming from Rooney, who lived the character, and David, who has such a keen eye for detail and quality."
"I have to say I'm a lucky girl right now," she added. "It's one of those things where my mom keeps reminding me, 'All your hard work is finally paid off.'"
"The Girl With the Dragon Tattoo" film opens in theaters nationwide on Dec. 21.