Cherop's first major competition was the 1999 All-Africa Games at the age of 15, but she did not make the podium, coming in fourth place. She was the bronze medallist over 5000 metres at the 2000 World Junior Championships in Athletics, finishing behind Dorcus Inzikuru and Meseret Defar. She started training with Sing'ore Girls, under running coach Boniface Tiren, and worked alongside other promising young runners, including future world champions Janeth Jepkosgei and Vivian Cheruiyot. A knee injury cut short her running season in 2001.