She is particularly noted for her collaborations with major 20th-century composers, such as Igor Stravinsky, Milton Babbitt, Pierre Boulez, George Perle, Sir Peter Maxwell Davies and her performances of great contemporary classical music by Arnold Schoenberg, Alban Berg, Anton Webern.
In a 1961 interview for Newsweek, Beardslee flaunted her unflinching repertoire and disdain for commercialism: "I don't think in terms of the public... Music is for the musicians.
About that performance, Alex Ross wrote in The New York Times that "the legendary soprano Bethany Beardslee-Winham, now well into her sixties, remains a compelling interpreter of new music."
In retirement, she was president of APNM (Association for the Publication of New Music) and produced a number of CDs of her own performances, as well as the compositions of her late husband Godfrey Winham, and her friend Arlene Zallman.
She has lived for the past thirteen years (as of when, the latest source is 2007) in a historic Georgian mansion, Maizeland, in the Hudson Valley, near her family.
He composed a number of pieces for Beardslee's sharp crystal soprano and dramatic wit, including: Du a Song Cycle for soprano and piano on the poetry of August Stramm, "Vision and Prayer: poetry by Dylan Thomas," Philomel text by John Hollander, "A Solo Requiem" in honor of her late husband, Godfrey Winham.
Craft, who conducted it, said to Beardslee that "your performance is the first that anyone can listen to beginning to end with total pleasure and belief in the sprechstimme medium.
In 1977–78, Rudolf Nureyev, dancing Tetley's choreography to Beardslee's live performances, appeared together in New York, Los Angeles, and Paris.