Doreen has been successful in many competitions. In 1995 she was the winner of the Dame Joan Sutherland Award for most promising newcomer in the Veronica Dunne International Singing Competition. She was a winner at the Bellini Festival in Sicily in 1997 and, later in the year, was the winner of the German Radio Prize at the Belvedere International Singing Competition in Vienna. In 1998 she was the winner of the RTE Young Singer of the Future, and winner of the West Belfast Classical Bursary. She was also a prizewinner in the John McCormack Voice of Athlone Competition, as well as being a prizewinner in the Lombard and Ulster Foundation Competition. Most recently, she was awarded the 2001 RNCM Doherty Recital Prize for Singing.

At the RNCM she sang the role of Meg in the 2001 production of Verdi's Falstaff, and this year took the role of Pauline in Tchaikovsky's Queen of Spades. In 1995 she sang the role of Dido in Purcell's Dido and Aeneas in the National Concert Hall, Dublin, and at Lismore County, Waterford, as part of the Early Music Festival. She repeated this role in a production for Lyric Opera, Broomhill. Other professional opera experience includes: Zoë, La Fiamma by Respighi, for Wexford Festival; Mercedes in excerpts from Bizet's Carmen; Lola in Cavalleria Rusticana; and the cover of Marcellina, Le nozze di Figaro, for Glyndebourne Touring Opera. She has sung as a member of the chorus for Opera Ireland, Scottish Opera and, most recently, Glyndebourne Festival Opera. This year she sang the role of Mercedes, Carmen, for Glyndebourne Touring Opera.

Doreen sings regularly in concert and oratorio, her repertoire ranging from Bach's St. Matthew Passion, Beethoven's 9th Symphony, and Verdi's Requiem, to Elgar's Sea Pictures. She has performed with the National Symphony of Ireland, the RTE Concert Orchestra, European Youth Orchestra and the Irish Chamber Orchestra. She also performs regular Lieder recitals throughout Ireland and England.

Doreen's studies at the National Opera Studio in 2002/03 were supported by a British American Tobacco Scholarship, The Goldsmiths' Company, The Friends of Covent Garden and the Peter Moores Foundation.