Williamson has won two medals at the World Archery Championships. In 1999 she finished with a silver medal, later calling it her "worst sporting moment" in an interview with "The Daily Telegraph" in 2004 after shooting below her expectations. In 2007 she and teammates Naomi Folkard and Charlotte Burgess secured bronze medal in the women's team recurve tournament, defeating Italy in the third-place match. By reaching the semi-finals they guaranteed a full berth of three female archers for the British team at the 2008 Summer Olympics.