Mewis co-captained the United States U-17 team that was runner-up at the inaugural 2008 FIFA U-17 Women's World Cup in New Zealand. Over the course of the tournament, Mewis scored two goals. She was the recipient of the Bronze Ball as the tournament's third-best player. Mewis also played in the 2010 U-20 Women's World Cup in Germany where the team lost in the quarterfinals. Mewis's younger sister Sam was also a member of both youth World Cup squads.