Lais da Silva Souza's first important competition on the Brazilian team was in the 2003 Pan American Games, where Brazil placed third in team competition, behind Team USA and Team Canada. That same year, in the 2003 World Artistic Gymnastics Championships, she was on the Brazilian team that qualified for the 2004 Summer Olympics. Team Brazil placed eighth overall in the 2003 World Artistic Gymnastics Championships. In her first Olympic Games, Team Brazil place ninth overall and da Silva Souza scored 9.387 on vault, 8.762 on bars, 9.375 on beam and 8.675 on floor.