[3] Her debut performance in South Africa was singing Handel's Messiah at the Johannesburg City Hall on 11 December 1951.

[3] Coertse made her debut in January 1955 as the "first flower girl" in Wagner's Parsifal at the Teatro San Carlo in Naples, Karl Böhm conducting.

[3] Coertse sang the soprano part in Bach's Matthäus-Passion at Fritz Wunderlich's first appearance in Vienna in 1958, when he performed the tenor arias with Julius Patzak singing the Evangelist.

[citation needed] In 1965, she sang Konstanze in Die Entführung aus dem Serail at the Vienna State Opera which also featured Fritz Wunderlich as Belmonte.

In 1966, Mimi was honoured by the President of Austria with the title Österreichischer Kammersänger, for her ten years of work as a permanent member at the Vienna State Opera.

She returned to the Vienna State Opera for a single farewell performance as Elisabetta in Don Carlo on 14 December 1978.

[5] This project has developed into the most exciting classical singing ensemble in South Africa, and is now on the brink of becoming a vibrant, new, young opera company.