[3] She was the second youngest of the six children of General Richard Mulcahy, who was a commander-in-chief of the Irish army and a government minister for Fine Gael and Mary Josephine "Min" Ryan, a founding member of Cumann na mBan.
She received an award from Elsa Schiaparelli in 1953 as part of the National Agricultural and Industrial Development Association show (NAIDA).
In 1955 she presented her first collection in the drawing room of her family home in Lissenfield, Rathmines, launching her career to great acclaim.
She used fine knitted or woven woollen materials by Michael McInerny, London, using bright colours that were more popular in the United States than Ireland.
Mulcahy also benefited from the success in the United States of fellow Irish designer, Sybil Connolly, with her exporting most of her output to American and German markets.
Mulcahy presented her 1967 collection on a transatlantic liner, and at a society luncheon fashion event in Chicago in 1968 her designs were exhibited.
She maintained her links with the Grafton Academy, judging graduating student collections, aiding in the development of a large number of upcoming designers.