Braun performed at the Metropolitan Opera for a brief period in 1949–1950 with her husband, Ferdinand Frantz, as a temporary replacement for Helen Traubel who had laryngitis.

Her early studies included roles such as the title character of Bizet's Carmen and Azucena from Verdi's Il trovatore.

[6] The opera was met with a hostile public response for its perceived anti-fascist themes and apparent influence of the German-Jewish composer Kurt Weill, as well as its unconventional musical elements.

[4] In reviews of the 1942 recording, critics later characterized Braun as a "better-than-average" Countess but ranked her performance below those of Elisabeth Schwarzkopf, Lisa Della Casa, and Kiri Te Kanawa.

[10][11] Braun was married to the German bass-baritone Ferdinand Frantz and accompanied him to New York City "just for the trip" when he sang with the Metropolitan Opera.

[15] Howard Taubman of The New York Times reported that the audience members, who were initially disappointed by Traubel's absence, were heartened by Braun's performance opposite Frantz, who sang as Wotan.

[5] Her guest performances included the Palais Garnier in 1950, the Teatro dell'Opera di Roma in 1952 as Brünnhilde, and the Opéra de Monte-Carlo in 1953 as Ortrud.