[5] O'Sullivan achieved her first major role in 1996 at the age of 34, as Donna Anna in Don Giovanni with Welsh National Opera.
The world renowned Australian soprano Dame Joan Sutherland helped O'Sullivan to prepare for the role.
In 1997 and 1998, O'Sullivan starred as the Queen of the Night in the Opera North performances of The Magic Flute.
[13] O'Sullivan had nodules removed from her vocal cords at the private Blackheath Hospital, London.
[19][20] Her death was marked by an outpouring of tributes to her talent and her outstanding contribution to music in Ireland and internationally,[19] with The Irish Independent stating that "[Ms O'Sullivan] was famed for her support of charitable events - and her sense of humour.
"[21] Following O'Sullivan's death, Cork Opera House announced plans to launch a programme in her memory designed to provide a platform to operatic singers in her name.
Among the objectives of this programme is to offer a platform to early career / emerging Irish opera artists for repertoire / role development, concert performances with orchestra, semi-staged performances and the curation of recital programmes that meets with their current and future repertoire ambitions.