The 49-year-old stars as sex surrogate Cheryl in the real-life story of how she helped paralysed journalist and poet Mark O'Brien, played by John Hawkes, to lose his virginity.
She told Stylist magazine: "Mark's disability is the thing that allowed the sex in this movie to be like the sex we all have; in a real way, rather than a choreographed, weird way. "There's no fancy lighting and music swelling. It's just happening; it's kind of extraordinary." The emotional nature of its story made the film easier for Helen, ridding her of any embarrassment at showing full-frontal nudity.
She explained: "I used Cheryl's desire to make [Mark] comfortable to balance the nerves. "She wanted him to know she was comfortable with her body to allow him to think, 'Maybe I can be comfortable with my body.' That helped; that got me through."
The film takes its story from How I Became A Human Being, the autobiography of Mark O'Brien, who was forced to wear an iron lung for most of his life after contracting polio aged six. It's a challenging role for Helen, who admits it is a definite departure from anything else she's done over her 40-year career.
She said: "[Cheryl is] unlike any real person I've played before. And I've played a lot."