In 1972, Esterman played the Madonna Vampyra in the ZBS Foundation radio play The Fourth Tower of Inverness, the first in the long-running Jack Flanders series. Esterman returned to ZBS in 1982 to star as the title character in the first Ruby the Galactic Gumshoe serial, and has reprised the role many times in the decades to come, most recently Ruby 10 in 2018. Many of her Ruby appearances are credited to a stage name, "Blanche Blackwell". Esterman also returned as the Madonna Vampyra in the 2000 sequel, Return to Inverness.