The 40-year-old actress, who initially went under the knife in 2013, directs and stars in the tense drama opposite her husband Brad Pitt, reported Us magazine.
"There were lots of scenes I wanted to change or cut. I realised it was going to be me (naked) in that bathtub. But I told myself, 'Put all of that aside... You can't change or cut this scene because you've had a mastectomy, or because we're married and people are going to analyse this or that. That would be cheating'," she said.