Her first major medal came at the 2004 African Championships in Athletics where she took silver in the 10,000 metres behind Eyerusalem Kuma.
She also won the Cursa de Bombers that year and repeated as the winner in 2005, setting a course record in the process.
She ran at the 2005 World Championships in Athletics and was tenth in the women's 10,000 m. Her 2006 season was highlighted by a win at the Vitry-sur-Seine Half Marathon.
Kwambai was selected to represent Kenya in the 10,000 m at the 2007 All-Africa Games and she won the bronze medal.
She was the silver medallist in the event at the 2007 World Military Games a few months later, where she was beaten by her national rival Doris Changeywo.