She established herself at the World Youth Championships in Athletics in 2001, winning the 3000 metres title. She moved to Japan several years later to compete for the Kyudenko running team. She has won several corporate track running titles for the team.
In 2006, she emigrated to Japan to take up professional running. She gained her first international selection soon after for the International Chiba Ekiden. Running in a team of Philes Ongori, Evelyne Kemunto Kimwei, Catherine Ndereba, Jane Wanjiku Gakunyi and Lucy Wangui Kabuu, she won the race and helped break the African record for the marathon ekiden distance.[4] The following year she competed on the Japanese track circuit and won the Miyazaki5K run.[5] She did not compete in 2008 and changed location for the 2009 season, entering a series of road races in Europe. Her best performances were a win at the Würzburg half marathon, third at the Kö-Lauf in a personal best 33:41 minutes, and a fourth-place finish at the Hamburg Half Marathon in another best of 75:27 minutes.[6]
In 2011, Chepyego took a 5000 metres/10,000 metres double at the Japan Corporate Championships,[6] but failed in her aim to make the 10,000 m team for Kenya at the 2012 Summer Olympics.[12] She was runner-up at the Sanyo 10K that year. She focused on the track event in 2013 and was rewarded with her first major international selection. After winning the 10,000 m at the Hyogo Relays, she placed third at the Kenyan trials. This earned her a place at the 2013 World Championships in Athletics. In the final she ran a personal best of 31:22.11 minutes, which brought her seventh place overall.[6] She won the Sanyo Half Marathon in December, setting a personal best and course record time of 68:24 minutes.[13]