For more than 20 years she baked her chocolate cakes, at first selling them in the city's Castro district out of a napkin-lined basket and then, after the onset of the Aids epidemic in the early 1980s, turning her kitchen into a veritable production line to ease the nausea and pain of patients in the terminal stages of their illness.
She called Aids patients her "kids" and, at the height of her activity, baked as many as 1,500 brownies a month with the money from her social security cheques, as well as the help of anonymous well-wishers who left clumps of marijuana on her doorstep.
She not only became a hero to San Francisco's gay community, but took up the broader cause of legalising marijuana for medicinal purposes. Thanks to her, the issue found its way on to a popular ballot in 1996, making California the first state to contemplate the medical use of soft drugs.
Born in Minnesota to an Irish Catholic mother oblivious to the druggy connotation the name Mary Jane was to have, she came to San Francisco during the Second World War with two girlfriends, found work as a waitress and married a soldier.
The turning-point in her life came in the early 1970s, when her 22-year- old daughter Jenny died in a car accident. With her marriage long since over and her only child gone, she reached out to the young gay men of the Castro and formed a near- maternal bond with many of them. The marijuana brownies started out as a way to make a living but evolved slowly into a cause.
Busted periodically for her activities, she spent hundreds of hours doing community service with Aids patients and, after experimenting to ease the pain of arthritis in her own knees, became the figurehead of the medical marijuana movement. By the time Brownie Mary was arrested in a friend's house in Sonoma County in 1992, her fame was such that the police did not dare press charges against her.
She published a book, Brownie Mary's Marijuana Cookbook, and was honoured by the city of San Francisco with her very own memorial day. Crippled by arthritis and wheelchair-bound after a fall last summer, she lived out her last few months in a nursing home. Her friend and lawyer, Larry Bittner, said: "Brownie Mary was a hero for our time, in a world with few heroes."
Mary Jane "Brownie Mary" Rathbun, drugs campaigner and charity worker: born Minnesota 22 December 1921; one daughter deceased; died San Francisco 10 April 1999.