Weightman won a world championship medal at the 2008 IAAF World Cross Country Championships and she and Benita Johnson helped lead the Australian women to the team bronze. She made her marathon debut soon afterwards, finishing thirteenth in the women's race with a time of 2:32:32. This performance gained her selection for the women's marathon race at the 2008 Summer Olympics, where she finished thirty-third with a time of 2:34:16, the second best Australian performance after Johnson.