After acting in several plays from 1966 to 1969, Miles was cast as Rosy in the leading title role of David Lean's "Ryan's Daughter" (1970). It was critically savaged, which discouraged Lean from making a film for some years, despite her performance gaining her an Oscar nomination and an Oscar win for John Mills, and the film making a substantial profit. In Terence Pettigrew's biography of Trevor Howard, Miles describes the filming of "Ryan's Daughter" in Ireland in 1969. She recalls, "My main memory is of sitting on a hilltop in a caravan at six in the morning in the rain. There was no other actor or member of the crew around me. I would sit there getting mad, waiting for either the rain to stop or someone to arrive. Film-acting is so horrifically belittling."