Riddell won the gold medal in the LW3,4,5 / 7,6 giant slalom competition, with a time of 2:41.35, better than opponents Karolina Wisniewska (2: 41.82) and Ramona Hoh (2: 42.06), at the 1998 Nagano Winter Paralympics.[3] In the LW3,4,6 / 8 downhill event, she finished second in 1: 15.00, behind her compatriot Jennifer Kelchner in 1: 14.97.[4] She won two bronze medals in the slalom (achieved time 2: 04.17),[5] and super-G LW3,4,5 / 7,6 / 8 (in 1: 05.80).[6]
At the 2002 Paralympic Winter Games in Salt Lake City, Riddell won the gold medal in the giant slalom LW3,4,9 (silver medal for Karolina Wisniewska and bronze for Lauren Woolstencroft),[7] and silver in the alpine super combined LW3,4,6 / 8,9 (in 1st place Woolstencroft and in 3rd place Wisniewska).[8] She placed in 4th place in the downhill category LW3,4,6 / 8,9; while on the podium were Rachael Battersby in 1: 30.63, Csilla Kristof in 1: 31.41 and Karolina Wisniewska in 1: 32.19.[9]
She finished second in giant slalom at the 2000 Hartford Ski Spectacular, behind Sarah Will.[10]