The film centres on the relationship between a Texas woman and a little Mexican girl who lost her family trying to cross the border illegally.

Cornish, who has appeared in varied films such as Bright Star, Sucker Punch and Limitless, plays Ashley, a single mum who had custody of her son taken away by social services.

About three-quarters of the The Girl's dialogue is in Spanish, a language the 30-year-old Australian never spoke before at all.

Looking for easy money, Ashley decides to act as a "coyote," or people smuggler, and helps a Mexican family illegally cross the border into the America.

But the venture ends in tragedy and Ashley is charged with caring for a little girl. 

"It was an experience that absorbed me completely," Cornish says in interview ahead of Friday's US premiere of the film.

"I gave up my personal life for five months.

"There was nothing else I could do. 

"But it was easy because I'm single, I have no kids, I live alone, and the truth is I'm a workaholic. 

"I don't have any other responsibilities."

For Cornish, her experience of shooting in Mexico left an indelible mark.

The actress video recorded her experiences on the set and, after editing more than 15 hours of material, posted parts of the footage on social media.