She was ranked number one in the world by the UCI in 2008,[7] and was one of the favourites to win the BMX women's event at the 2008 Summer Olympics in Beijing, in the end she finished fourth.

[8][9] At the 2010 BMX World Championship in Pietermaritzburg, South Africa, Walker finished second in the Elite Women's event, with first place going to Shanaze Reade.

[12] At the September 2014 UCI BMX Supercross World Cup race in California, Walker had a fall and suffered a serious head injury.

[13] Whilst her helmet cam recorded her calmly giving detailed accounts to medical staff of what happened to her, she has no recollection of the entire day.

[6] She missed being nominated for the 2016 Summer Olympics in Rio de Janeiro due to breaking her arm during training in February 2016.

[6] 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.