[1] Born Dorothy Ann MacGregor (later adopted the name McIlraith)[2] in Toronto, Ontario, Protero studied singing with James Rossellino in her native city from 1949 through 1959 and her first professional performing experiences were with his Rosselino Opera Company during the early 1950s as Annina in performances of Giuseppe Verdi's La traviata.
She was also a pupil of Toti dal Monte in Venice (1955–1957), Ferdinand Grossmann in Vienna (1957), Lorenz Fehenberger in Munich (1963), and in New York City with Rosa Bok (1967–1970) and Oren Brown (1975–1976).
[2] She made her European opera debut in 1955 as Papagena in Wolfgang Amadeus Mozart's The Magic Flute at the Teatro di San Carlo.
[1] She sang Papagena at the Glyndebourne Festival in 1960 and that same year made her first appearance with the Canadian Opera Company (COC) as Ciboletta in Johann Strauss II's Eine Nacht in Venedig.
She returned to the COC numerous times during her career, portraying such roles as Gretel in Engelbert Humperdinck's Hänsel und Gretel (1962, 1963), Musetta in Giacomo Puccini's La bohème (1965), Parasha in Igor Stravinsky's Mavra (1965), Oona in the world premiere of Raymond Pannell's The Luck of Ginger Coffey (1967), Rosina in The Barber of Seville (1970), and Marzelline in Ludwig van Beethoven's Fidelio (1970).