Making her senior international debut, Kostner won gold at two September events, the 2002 Nebelhorn Trophy and 2002 Ondrej Nepela Memorial. In January, she finished fourth at the 2003 European Championships in Malmö, Sweden. In March, she became the first Italian skater to medal at Junior Worlds. Ranked first in her qualifying group, first in the short program, and fifth in the free skate, she took bronze at the 2003 World Junior Championships in Ostrava, Czech Republic.