In her youth, Chepkirui competed in age category competitions. She defeated Yuriko Kobayashi over 1500 m at the 2005 World Youth Championships in Athletics to claim her first international gold medal. Her finishing time of in a 4:12.29 minutes was a championship record. She returned to defend her title two years later, but ended up as bronze medallist at the 2007 event. She failed to improve at the 2008 World Junior Championships in Athletics and did not get past the heats. She dropped out of the sport after that year.