The Titanic star decided to take a break after the draining project, so she can spend quality time in her adopted New York with her two children and husband Sam Mendes.
She explains: "Sarah is the hardest part I've ever had to play. The emotional journey the character Sarah goes on is epic - epic for a woman?Sarah is isolated, depressed.
"She feels she lost herself through having a child and marrying the wrong man. She resents the child and has made terrible errors of judgment.
"The challenge was to embrace playing someone so weak."