Martin Scorsese's new film tells the story of former mob boss Frank Sheeran, who claims to have murdered labour union chief Jimmy Hoffa, who vanished without a trace in 1975 and was declared dead in 1982.
De Niro stars as Sheeran in the movie, opposite Anna as his daughter Peggy.
Following Jimmy's murder, Anna's Peggy asks Robert's Sheeran, "Why? Why?" When he replies, "Why what?", she says, "Why haven't you called Jo?"
Those are the only words Anna says in the whole film, which many fans have criticised - accusing bosses of underusing the talented, Oscar-winning actress.
However, in a new interview with USA Today, Robert insisted he thought Anna's portrayal of Peggy was perfect for the film.
"She was very powerful and that's what it was," he said. "Maybe in other scenes, there could've been some interaction between Frank and her possibly, but that's how it was done. She's terrific and it resonates."