The 37-year-old actress struggled to portray Winnie Mandela in 'Mandela: Long Walk to Freedom', which was released last month, reported Contactmusic.
"I was terrified at the mountain I had to climb to play this woman and discover who she is. It's definitely the hardest role I've ever played in my career," Harris said.
However, the star insists meeting her alter-ego in person helped her get into the role more.
"It helped me enormously (meeting her). I asked her how she wanted to be portrayed and I fully expected her to say, 'I want to be portrayed as a saint, as Mother Africa.' But she didn't. She said, 'You do your research, and all I ask is that you play me truthfully," she added.