Mullen was in her mid thirties when she was confined to a wheelchair following complications resulting from an epidural. She started attending the Clontarf day centre of the Irish Wheelchair Association in the mid 1980s, where she was introduced to lawn bowls, for which she proved to have a natural aptitude. She won the national special bowls novice title in 1985, winning the Irish senior titles in 1986 and 1987, making her the first bowler from the Republic of Ireland to do so. She took part in the Stoke Mandeville Games in 1986 and 1987, winning bronze in the singles and doubles events. She trained in Northern Ireland in preparation for the 1988 Paralympic Games in Seoul, Korea, training against and often defeating top able-bodied players.