PYEONGCHANG, South Korea — When the North Korean leader, Kim Jong-un, decided to send a large delegation to the Winter Olympics in South Korea this month, the world feared he might steal the show.

If that was indeed his intention, he could not have chosen a better emissary than the one he sent: his only sister, Kim Yo-jong, whom news outlets in the South instantly called “North Korea’s Ivanka,” likening her influence to that of Ivanka Trump on her father, President Trump.

Much as Ms. Trump has been when traveling with her father, Ms. Kim was closely followed by the news media during her three-day visit to Seoul and to Pyeongchang, which is hosting the Olympics. She flew back to North Korea on Sunday night.

Flashing a sphinx-like smile and without ever speaking in public, Ms. Kim managed to outflank Mr. Trump’s envoy to the Olympics, Vice President Mike Pence, in the game of diplomatic image-making.