Hedman, who had been a well-known model, arrived in Italy as wife of an Italian Journalist, Paolo Frajese, who in 1965 had gone to Sweden for a number of television reports. In 1976 she made her film debut with a small uncredited role in Lucio Fulci's sex comedy La pretora (My Sister In Law), starring Edwige Fenech. Later in 1976, she played a minor role in Emanuelle in America, appearing in her first hardcore scene. Then Hedman also appeared in the RAI show Carosello and posed for the Italian issue of Playboy Magazine. In 1979 she played a major role in Joe D'Amato's Immagini di un convento ("Images in a Convent"), an adaptation of La Religieuse.

Throughout the late 1970s and early 1980s, Hedman had supporting roles in mainstream films such as Primo Amore (1978) for Dino Risi and La città delle donne (City of Women) (1980) for Federico Fellini, as well as leading roles in pornographic cinema, in which she was considered one of the first Italian divas. 1984 and 1985 were prolific years for her, playing in films named after her, such as Marina e la sua bestia (Marina and her beast). She also played opposite John Holmes in the film The Devil in Mr. Holmes (1987). She appeared in her last film in the early 90s.