Jacqui Graham said that Howard died Thursday at her home in Bungay, England. No details as to the cause of death were immediately available.
Howard's whirlwind life saw her write 15 novels, leave three marriages, model, act, broadcast, and much more. Many of her books were critical successes, but she was best known for "The Cazalet Chronicles," which followed the tangled lives and loves of several generations of an aristocratic household in the run-up to World War II.
Graham described Howard—who went by Jane—as "remarkably odd, and interesting, and fabulous, and brave."
"She walked away from a marriage, which was a very advantageous one, to do what she wanted to do, which was write. She lived her life in a way that she wanted to live it in, in a way that women at that time just didn't have the nerve. She had the nerve."
Born in 1923, Howard had little in the way of formal education, but she read voraciously—"huge amounts of Shakespeare and other classics," Graham said. "When she ran out of stuff she wrote her own things."
Howard married at age 19 to Peter Scott, the son of Capt. Scott, the famous polar explorer, a wedding which would mark the start of a long and tumultuous love life.
"As she put it herself, Jane was a bit of bolter," Graham said. "She didn't put with up things she wasn't going to put up with."
Howard's work included "The Beautiful Visit," a coming-of-age novel structured around World War I, and "Mr. Wrong," a collection of short stories centered on the lives of 1960s London women, and "The Cazalet Chronicles," a series of books which would follow the eponymous upper-crust dynasty from the carefree '30s, into World War II, and beyond.
"It preceded, by a long way, 'Downton Abbey,'" said Graham. "People love reading family sagas set slightly in the past—not too far back (but) close enough for you to touch, within living memory. She unconsciously got that long before ('Downton Abbey' creator) Julian Fellowes."
Howard's literary legacy also lives on through her stepson, writer Martin Amis, who credited her with steering him away from comic books and on to more serious reading.
Funeral arrangements weren't immediately available. Howard is survived by Nicola, her daughter from her marriage to Scott.