Coulson was married to actor Jack Nance (who played Henry Spencer in Eraserhead, and Pete Martell in Twin Peaks) in 1968; they divorced in 1976. Her second husband, Marc Sirinsky, with whom she had a daughter, Zoey (born 1987), is a rabbi, at one point resident at Temple Emek-Shalom in Ashland, Oregon.

Coulson met Lynch in 1971 and performed various behind the scenes functions during the four-year filming of his low-budget classic Eraserhead (1977). Lynch reports that she began meditating at the same time as did he during this period. She also appeared in Lynch’s short film The Amputee (1974), in which she played a woman with no legs.

Coulson appeared in “Dual Spires”, a 2010 episode of Psych that spoofed Twin Peaks. In 2012, she appeared in the second season of Portlandia.

On September 28, 2015, Coulson died of complications from cancer at her home in Ashland. The first episode of the revived Twin Peaks was dedicated to Coulson and the fifteenth was dedicated to her character, Margaret Lanterman.

Coulson went on to reprise her role in the film prequel, Twin Peaks: Fire Walk with Me, and in the 2017 revival. In the new series, her character (the Log Lady) appears in the first, second, eleventh, and fifteenth episodes, where she passes on a message from her log for Deputy Hawk to resume the search for Agent Cooper.