In his book The Last Prima Donnas, music critic Lanfranco Rasponi included Fenn in his list of American divas "who showed so much promise (all were talented and had good basic vocal resources) only to go into limbo".

[4] A 1967 live recording of her performing the title role in Tosca with Richard Tucker as Cavaradossi at the Academy of Music in Philadelphia was released by Lyric Distribution ALD in 1989 and again in 2000 by House of Opera.

While there she studied voice with Florence Holtzman and participated in the opera theatre program which was run by renowned Russian tenor Vladimir Rosing.

[7] She made her debut with the San Francisco Opera on October 10, 1952 as Musetta in Puccini's La Bohème with Bidu Sayão as Mimì, Jan Peerce as Rodolfo, Frank Valentino as Marcello, and Gaetano Merola conducting.

She later returned to that house in 1955 to sing two roles with the company, Oxana in Tchaikovsky's Cherevichki (performed under the title The Golden Slipper) and Violetta in Verdi's La traviata.

[1][7] In 1953, Fenn joined the roster of principal sopranos at the Metropolitan Opera, making her debut with the company on November 11 of that year as Musetta to the Mimì of Hilde Güden, Rodolfo of Eugene Conley, and Marcello of Robert Merrill.

[8] After a two-year absence from the Metropolitan, Fenn returned in April 1959 to portray Rosalinde in Die Fledermaus by Johann Strauss, with Theodor Uppman as Eisenstein and Laurel Hurley as Adele.

[9] That same year she performed her first lead Wagner role at the house, portraying Eva in Die Meistersinger von Nürnberg, with Paul Schöffler as Hans Sachs.

She was a regular performer with the Los Angeles Civic Light Opera (LALCO) during the 1950s and 1960s, and a personal close friend of that company's director, Edwin Lester.

She notably starred as Verity Craig in the original production of Noël Coward's Sail Away when it opened in Boston in 1961 before its New York run.

In 1969, she portrayed Queen Isabella in the world premiere of Meredith Willson's musical 1491 at the LALCO with Chita Rivera as Beatriz and John Cullum as Christopher Columbus.