Actress Lupita Nyong'o delves into the heartbreak of the antebellum South in "12 Years a Slave"

(FOX SEARCHLIGHT PICTURES) -  In preparing for her first film role as a petite, hard-laboring slave in "12 Years a Slave," actress Lupita Nyong'o sized herself up against 500 pounds of cotton, which her character Patsey picked every day.

Nyong'o's performance one that has generated critical acclaim for the Hollywood newcomer and predictions she will earn a best supporting actress Oscar nomination.

Patsey has the unfortunate lot of not only being a slave but also the object of love and sexual desire of her master, the cruel and conflicted Edwin Epps played by Michael Fassbender.

Nyong'o was born in Mexico 30 years ago (hence the Mexican name Lupita) where her Kenyan father was in political exile, but they moved back to Kenya when she was 1. She was educated in the United States and was graduating from Yale University's School of Drama just as she prepared her first-ever audition tape for McQueen's film.

After a grueling audition with a Hollywood casting director, Nyong'o then auditioned in person for McQueen in Louisiana. He called her the next day.

"He said 'Hello, this is Steve McQueen and I would like to offer you the role of Patsey,'" Nyong'o told Reuters.

"My knees grew weak and I sat on the pavement and I said 'I'd like to accept the role of Patsey,'" she added.

Nyong'o admits to being "very" intimidated by the experience and expectations of her director and fellow cast members and was thinking that any day she would get the call saying there had been a mistake.

But she had six weeks to prepare and set about reading accounts of slavery from the female perspective and visiting museums to get a three-dimensional idea of what life on the plantation was like. She had both a script and an autobiography to learn about Patsey.

Patsey is a complex character, lofty yet vulnerable, a woman who looks like a child, a productive superhuman treated like an animal. Many of the film's most wrenching scenes involve Patsey being subjected to unspeakable physical and emotional torture.

"There was an underlying stream of grief at all times even in the lighter scenes," Nyong'o said. "There is a deep pain in Patsey throughout and living in that pain was not easy."

In the week before filming began, Nyong'o found herself daydreaming about Patsey and wondering what she would have done with the very little free time she had.

She conjured up the idea of making corn husk dolls for little girls on the plantation. After Googling to confirm that it was historically accurate, she learned how to do it herself.

"There was always something very childlike about Patsey for me because I know she had been robbed of her childhood by her master taking an early sexual interest in her," Nyong'o said.

She said McQueen used the doll-making to show the part of Patsey that could not be enslaved.

"That was really powerful for me," Nyong'o said. "In playing her, I learned that you don't have to live a day free to know what freedom is."

"12 Years a Slave" opened in the United States on October 18. Oscar nominations are announced January 16, 2014.