She had an elder sister, Elsie Wallace MacDonald, who had also been a vaudeville performer and then operated a dance school until 1962.

[citation needed] Rock adopted the name Marie Blake for her film career, beginning as a Metro-Goldwyn-Mayer contract player in 1937 with an uncredited appearance in My Dear Miss Aldrich.

Her first credited major part was Love Finds Andy Hardy (1938), and she then played her most notable onscreen role as Sally, the hospital switchboard operator, in the nine films that comprised MGM's popular Dr. Kildare series from 1938 to 1942.

[1] Rock returned to using her real name in the 1950s, and later gained her biggest fame by playing "Grandmama" on the ABC sitcom The Addams Family, which was originally broadcast from 1964 to 1966.

[1][7] Rock suffered a stroke in December 1967 that affected her speech and prevented her from reuniting with fellow castmates for the 1977 television film Halloween with the New Addams Family.