In 2004, Simpson became African Champion and followed this result with a ninth place finish at the 2004 Olympics. In 2010 she participated in various international competitions, among which are; the Commonwealth Games and the Senior African Championships. She won the 17th edition of the African Championships with 6031 points.
During the Commonwealth Games in Delhi, India she picked up an injury that prevented her from successfully ending the competition where she was in the top three.
However she came back in great form the following year and won the 2011 edition of the Multi stars meeting in Desenzano del Garda with a score of 6270 points (world leading performance at that time of the 2011 season), defeating the 2010 champion Marina Goncharova.
Simpson is renowned for her strong javelin throw, her personal best in which is 56.36m, and she is a good medal prospect in view of the World Championships in Daegu, South Korea.