Born in Ewell, Surrey, Strachan grew up in Hinchley Wood and attended Chadsworth Stage School, then Claremont Fan Court School, both in Esher. In her teens, she suffered from anorexia. Later, while at ArtsEd, London, she briefly held jobs as an Avon lady and as a kissogram. After her years at ArtsEd, Strachan performed in theatre, before moving on to children's television.