Competing at the senior level, Štefečeková won her first medal at the 2003 World Championships, where she finished third. After placing 10th in 2006, 9th in 2007 and 6th in 2009, she won the gold medal at the 2010 World Championships, with 72 hits in qualification and 19 in final, beating Liu Yingzi and Jessica Rossi. She added a silver medal in 2011, where only Liu Yingzi defeated her and a bronze medal in 2017. Her biggest success came at the 2018 World Championships, where she won the gold medal not only in the individual event, defeating Wang Xiaojing in the final shoot-off, but also in the mixed trap with Erik Varga.