Simpson reached the global podium for the first time at the 2005 World Championships in Athletics, taking third place with the second best performance of her career with a tally of 6375 points. She had set a personal best of 6423 points at the Hypo-Meeting earlier that season. She missed the 2006 season but returned the year after with a gold medal performance at the 2007 All-Africa Games. She failed to finish at the 2007 World Championships in Athletics later that season. She missed all of the 2008 season after this. She was off form in 2009 and registered a season's best of 5872 points at the Meeting International d'Arles. She was back to good form at the 2010 African Championships in Athletics, where she won a third heptathlon title in a score of 6031 points. She also managed eighth in the high jump for African at the 2010 IAAF Continental Cup.