[4] She attended Barnard College but dropped out in 1947 to marry Michael Henry Irving (1923-2003), a Harvard graduate who served in the Navy.
[2] Biddle once rode in the trunk of a Ringling Bros. and Barnum & Bailey Circus elephant on Madison Avenue in a nationally publicized stunt to help acquire Cirque Calder into the museum's permanent collection.
[2][9] She also oversaw the moving of the museum into the Marcel Breuer-designed structure on 945 Madison Avenue in the Upper East Side.
[10] She divorced Irving in 1979 and married Sydney Francis Biddle (1918-2004), a lawyer turned artist trained at Harvard College and Columbia Law School.
Her daughter, Fiona Donovan, a Barnard College and Columbia University-trained art historian,[14] served as trustee until 2003.