She has been a princess, a populist, a feminist. A fashion designer, an author, a wife, a mother. And an icon. But right now Diane von Furstenberg has a toothache. “I had some dental work,” she says, seated on a sofa at her New York City headquarters beneath an eight-foot-long portrait of her by Francesco Clemente. “I can’t believe I had my picture taken. My mouth feels so swollen.” Of course, she’s astonishingly beautiful; in 1972 this magazine wrote, when she appeared on the cover with her then-husband, that she glowed “with the sultriness of a Biblical temptress.” Assistants from the photo shoot bustle in and out, and her 19-year-old granddaughter, Talita (properly styled she’s Talita Natasha Prinzessin zu Fürstenberg), pops her head in to say goodbye; she’s catching the…