She began her athletic career in 1974, joining Haslemere Border AC as their first female member.
Armstrong met Nigel Gates, a fellow athlete, in 1979 at an international race in Manresa, Spain, and they married in 1982.
For the majority of Armstrong's international career they lived and worked together in Bath, having founded Springs Health Club in the city.
Throughout her early athletic career, Armstrong suffered from an eating disorder and this is documented in her book, Running to Learn.
In April 2008, Armstrong published her first book, Running to Learn, which offers a mix of autobiography and the ideas and philosophy behind her successful career as a therapist.