Schmitz made her debut for the German under-15 national team in 2007. In 2008, she was part of the under-17 team that won the UEFA Under-17 Championship and finished third at the FIFA U-17 World Cup later that year. Being third choice goalkeeper behind Anna Felicitas Sarholz and Almuth Schult she wasn't used in any of the matches during both tournaments though. In 2011, she was called up to the German squad that won the UEFA Under-19 Championship and played in 4 matches at the final tournament.