COPENHAGEN—A 14-year-old girl died Thursday at a popular amusement park in northern Denmark, police said, reportedly when the rear part of a roller-coaster ride came off the rails. A 13-year-old boy suffered injuries to one hand, police said. Henrik Ragborg Olsen, manager of the Tivoli Friheden amusement park in Aarhus, Denmark’s second-largest city, told local…