Fashion: After the Twig, the Tree?

Her mother calls her "Legs," which is, after all, as good a nickname as any for a girl whose 5-ft. 10-in., 105-lb. body is supported on what appear to be stilts, moored at the bottom to size 8½ feet. With a physique like that—and an oval face with fathomless, huge brown eyes to go with it—it was perhaps inevitable that Penelope Tree, 17, should emerge as the brightest new model and the likely successor—at least conversationally—to Twiggy.

Penelope, daughter of wealthy English Businessman Ronald Tree and former United States Delegate to the United Nations Marietta Peabody Tree, likes being a...