I’ve found (i.e., been sent) a quote from The Girl With The Dragon Tattoo extra Donald Josephson in a recent article in Sweden’s Dagens Nyheter. Here’s a crude Google Translate version, and here’s the excerpt:

“The most fun was to keep up with Rooney Mara in the green room, where the actors wait between shots…and [to] hear her anxiety over whether she would be better than Naomi Rapace. She had lots of those ‘mirror mirror on the wall’ moments in there. Mara asked her assistant all the time, ‘Do we not do better when we did this scene? Do I not look better than her? Am I not better? Am I not young? Are not I cool?’ And the assistant just replied, ‘Yes, yes, yes! You’re the best, you’re the best!'”