Harriet Holliday sparkled with personality. She reminded Kevin Horowitz, her third husband, of the mother in Mamma Mia!—free-spirited, flamboyant and nurturing. She dressed with a sexy, sophisticated glamour and regaled friends with witty tales at soirees. As hospitality manager at a winery in Napa Valley in California, she planned events for hundreds of guests. But around six years ago, at age 49, Holliday “started turning mean,” Horowitz recalls. “She didn’t know when to hold her tongue.”