Riddles was born in Madison, Wisconsin to Willard and Mary Riddles, and moved to Alaska just before her 17th birthday. She saw a sprint race and fell in love with mushing. Her first race was the Clines Mini Mart Sprint race in 1978, when she won first place. After finishing 18th and 20th in the 1980 and 1981 Iditarod races, she decided to breed her own sled dogs in order to advance. She moved to Shaktoolik, Alaska and worked as a fish seller for a short period while training her dogs, then moved to Teller, Alaska where she met Joe Garnie; they became partners and started breeding and training dogs together.
On March 20, 1985 Riddles won the Iditarod Trail Sled Dog Race, the first woman to do so. After winning the race, she wrote three books about her adventures and also became a professional speaker. In 2007, her Iditarod Trail Race victory was inducted as a "Hall of Fame Moment" into the Alaska Sports Hall of Fame.
After winning the Iditarod, she also decided to live like an Alaska Native for six years.