Walker wanted to become an Olympic athlete ever since watching New Zealand swimmer Danyon Loader receiving his gold medals at the 1996 Summer Olympics. She was about to start track cycling and quit BMX when it was announced as an Olympic sport for the 2008 Summer Olympics in Beijing, and this was the first Games she attended, competing in the women's BMX. In the medals race, she ran a time of 38.805, finishing fourth. In the same event at the 2012 Summer Olympics she got a silver medal, with a time of 38.644. She missed being nominated for the 2016 Summer Olympics in Rio de Janeiro due to breaking her arm during training in February 2016. During the Rio Games, it was announced that she had been elected onto the IOC Athletes' Commission; whilst initially missing out to Yelena Isinbayeva, president Thomas Bach proposed that Walker be added to the group.