With 213 acting credits to her name, Mary Treen was an accomplished character actress, known best among Lifers (fans of It's a Wonderful Life) as Cousin Tilly. Just like her brother Eustace, and Ma and Pa Bailey's maid Annie, Tilly's job was to bring levity to the film during the heavy scenes, and to show exactly how dire the situations were simply by the expressions on her face.
Treen's first acting job was a short film called Surprise in 1930. Her last acting job was a TV movie called Wait Till Your Mother Gets Home in 1985. In between, she appeared in the films Kitty Foyle (1940) and Room for One More (1952). I can honestly say I have not seen any of these movies...for better or for worse.
She also spent a great deal of time acting for the small screen, making appearances on The Love Boat, Happy Days, Laverne and Shirley, The Brady Bunch, and if you can find it anymore, The Dukes of Hazzard, as Aunt Clara Coltrain.
Treen was born March 27, 1907. She died July 20, 1989, in Newport Beach, CA. She was cremated and her ashes scattered.
Sources: IMDB, Find a Grave