Jackson, who was a model of Robert LaVigne's, gained Beat notoriety from having an affair with Kerouac's muse, Neal Cassady. She killed herself by slitting her throat and throwing herself off the roof of 1051 Franklin Street (reached from her apartment's roof at 1041) in San Francisco, supposedly over her fear of the consequences from having impersonated Neal's wife, Carolyn, to help Neal get money from the bank for a race track betting scheme. Kerouac describes Jackson's death in The Dharma Bums Chapter 15 thus:
The musicians and I drank up all the wine and talked, till about midnight, and Rosie seemed to be all right now, lying on the couch, talking, even laughing a bit, eating her sandwiches and drinking some tea I'd brewed her. The musicians left and I slept on the kitchen floor in my new sleeping bag. But when Cody came home that night and I was gone she went up on the roof while he was asleep and broke the skylight to get jagged bits of glass to cut her wrists, and was sitting there bleeding at dawn when a neighbor saw her and sent for the cops and when the cops ran out on the roof to help her that was it: she saw the great cops who were going to arrest us all and made a run for the roof edge. The young Irish cop made a flying tackle and just got a hold of her bathrobe but she fell out of it and fell naked to the sidewalk six flights below. (Penguin Books, 1976, p. 112)
Note that I reported she cut her throat but Kerouac said wrists. I depended on Gerald Nicosia's Memory Babe: A Critical Biography of Jack Kerouac for the throat detail (University of California Press, 1994, p. 499). And it seems Natalie didn't necessarily throw herself off the roof, but may have accidentally fallen off while backing away from the police officer who attempted to grab her. It's hard to say if she would have survived cutting herself had the police been successful in preventing her fall.
Either way, Natalie died tragically and too young, one of several Beat figures to do so (e.g., Bill Cannastra and David Kammerer).
RIP, Ms. Jackson.