It was in the field of cross country running that she gained her first major junior medal, running at the 2000 IAAF World Cross Country Championships. Timbilil took the silver medal behind Vivian Cheruiyot, completing a Kenyan sweep of the medals which led the junior women to the team gold. At the age of seventeen, she gained selection for the 2000 Sydney Olympics and reached the 10,000 m final, finishing in fourteenth place with a personal best run of 31:50.22. She was still eligible for the junior competition at the 2001 IAAF World Cross Country Championships, but she was far from medal-winning form and finished in sixteenth place.