Mary Thomas O'Neal moved to Los Angeles later in life, and opened a clothing shop. After World War II she visited Wales again, with her second husband. In 1950 she attended a union commemoration at the Hollywood Palladium, and in 1965 she spoke at a memorial program at Ludlow. She wrote a memoir, Those Damn Foreigners (1971), considered the only "published eyewitness account of the Ludlow massacre." She lived in the Hollywood Knickerbocker Hotel as an old woman, and experienced memory loss before she died, probably in the 1970s.