Complex sentence: In 1902 she became the first woman to compete at the World Figure Skating Championships by entering what was presumed to be a men's event, winning the silver medal, which prompted the International Skating Union to institute a separate ladies' event.
Split into simpler sentences: In 1902 she became the first woman to compete at the World Figure Skating Championships by entering what was presumed to be a men's event. She won the silver medal, prompting the International Skating Union to institute a separate ladies' event.