I don't understand how can Rooney Mara act in four movies in one single year, can you tell me how she does it?
Well, first of all, she didn't act in all of them in THIS year. Nor, I imagine, did she act in all of them in one year.
Youth in Revolt was released in September, 2009
A Nightmare on Elm Street released in April, 2009
Kaboom was premiered at Cannes in May, 2010
The Social Network will be released in October, 2010
The release dates of the movies alone span more than a year. And who knows when they were even filmed! Some movies take longer in post-production, depending on the special effects, if the distribution studio takes more time to raise money, etc. etc. etc.
Filming for those movies could have happened in 2007, 2008, parts of 2009... (For example, Youth in Revolt filmed in the summer of 2008, and was shifted around the release schedule for about a year.)
Plus, a lot of movies only take about 5-6 weeks to film. The actors are not involved in post-production except to do looping. Then they promote the film if/when it's released. There are 52 weeks in a year, so 5-6 weeks is not a HUGE commitment!
How much nudity will Rooney Mara do in the Girl With the Dragon Tattoo?
Most actresses have something in their contracts regarding how much nudity they are willing to do for a movie or tv show role.
So, regardless of what is in the book or not, it depends on how much Mara is committed to do for the role and contract stipulations.