SARAH JESSICA PARKER is busy. While raising three children—twins Tabitha and Marion Loretta are 8, son James Wilkie is 15—with husband Matthew Broderick, the actress and entrepreneur produces and stars in the HBO series “Divorce”; serves as vice chairman of New York City Ballet; has a line of shoes, handbags and a little black dress called SJP Collection as well as a bridal line with Gilt; runs a fiction imprint at Hogarth, a literary division of Penguin Random House; and also designs women’s and children’s clothing for the Gap. On top of that, “Blue Night,” a new film in which she portrays a jazz singer (and appears...