Kelly competed in sand volleyball for University of Southern California, after graduating high school a semester early to join the team in the spring of 2014. Her freshman season (2014) she played with Alexa Strange, finishing with a 33-7 record. As a sophomore (2015), she paired with Sara Hughes and the duo went 44-3, winning the last 25 matches of the season. They won the AVCA National Championship, with Claes being chosen AVCA All-American. Claes completed a perfect junior season (2016), finishing 48-0 in matches and losing only one set with Hughes. Her final season as USC (2017), they won the National Championship again and for the second straight year Claes was named AVCA All-American.
In her first year (2017) on the AVP as a true beach volleyball professional (Claes and Hughes played in AVP tournaments during their college years but didn’t accept their winnings due to NCAA), Claes won her first tournament at the AVP Gold Series // Championships in Chicago with partner Sara Hughes, becoming the youngest team to ever win an AVP event.