As with most Hollywood biopics, there are liberties taken with the real story, most notably in that Margaret (Molly) and J.J. never reconciled. They separated in 1909, although they remained good friends who cared deeply for each other until his passing. She was also not quite the social outcast depicted in the film. Other aspects of her life that were missing from the movie: they had two children, a son and daughter. Margaret Brown was a passionate social crusader and philanthropist; she was a champion of women's rights, including education and the vote. She championed workers' rights, historic preservation, education and literacy, and child welfare, including helping to found the modern juvenile court system. After the sinking of the Titanic, she was noted for her efforts to commemorate the heroism of the men aboard the ship. After WWI, she helped to rebuild France and to aid wounded soldiers, and received the French Legion of Honor. She also ran twice for the U.S. Senate. She died in 1932.
The sequence where J.J. Brown accidentally burns his money after Molly has hidden it in the stove didn't really happen. It was made up by a Denver journalist, after Molly Brown became a hero on the Titanic. When her daughter asked why she didn't refute the false story, Molly Brown supposedly replied, "It's better that they write *something* about me than nothing." (Kathy Bates, as Molly Brown, repeats the story in James Cameron's Titanic (1997).) Molly Brown is also said to have reported the story with a slightly different ending. Molly did hide money in the potbelly stove in their Leadville cabin, and Johnny unknowingly started a fire on a particularly cold night. According to Molly, as reported in newspapers interviews during her lifetime, "Just think if it had been paper money!" The money was gold and silver coins, which melted and adhered to the stove. Miners didn't trust paper money in those years. The stove had to be broken apart and resmelted to separate the iron, gold and silver.
Margaret Brown was in Paris visiting daughter Helen when she got a cable alerting her that her infant grandson was very ill. She cut her visit short and hurriedly caught the earliest ship home -- thus, she was very much an accidental passenger on the Titanic.