Brunette, with large eyes and a deadpan manner, Ms. Cooper excelled at comedy. It wasn't easy drawing focus away from Lauren Bacall, the star of the John Kander and Fred Ebb musical (which was based on the Tracy-Hepburn film of the same name), but Ms. Cooper managed to do it as Jan Donovon, the drab ex-wife of Sam Craig, the Tracy character. She stopped the show with her punchlines in "The Grass Is Always Greener," a duet with Bacall's character, Tess Harding, in which the two women envy the circumstances of one another's lives. Ms. Cooper stole the number, sending the audience into gales of laughter with her nasal refrain "What's so wonderful?" Ms. Cooper also won a Drama Desk Award for her work. She would later tour with Bacall in the show, and toured again, in 1984, this time with Barbara Eden.

Source: playbill.com