This unpublished illustration by Hilary Knight features Eloise slumped in a chair in the Plaza's enormous, opulent lobby. (Collection of Hilary Knight, © Kay Thompson) NEW YORK —Sixty years after she captured America's heart, six-year-old Eloise is still making trouble at the Plaza Hotel in New York City. Eloise is the central character in a series of beloved children’s books, written in the 1950s by Kay Thompson, who died in 1998, and illustrated by Hilary Knight, who’s very