"They told me an actual 12-year-old [Lilla Crawford] would play Little Red Riding Hood," she told ET at the Into the Woods New York premiere on Monday. "In the show it's a grown woman, so I was like, 'Put me in! I can do it!'"
Based on the Broadway musical, Into the Woods follows the classic tales of Cinderella, Little Red Riding Hood, Jack and the Beanstalk and Rapunzel, when a baker (James Corden) and his wife (Emily Blunt) want to begin a family despite their interaction with a witch (Meryl Streep), who put a curse on them.
"This was a dream come true," said Anna. "When I found out that they were making this into a movie, I just hoped and prayed and wished and wished, and it's such a gift. I feel forever grateful to [director] Rob Marshall."
While she couldn't have asked for a better project, the role didn't come without difficulty. Anna told us that she had one of the toughest songs in the movie.