Au represented Hong Kong at the 2012 Summer Olympics in London, where she competed in the women's individual sabre event. She lost in the first round to Tunisian fencer and two-time Olympian Azza Besbes, with a final score of 13–15. She reached the table of 32 at the 2014 World Championships in Kazan after defeating Venezuela's Alejandra Benítez, but lost to eventual bronze medallist Vassiliki Vougiouka of Greece.