She was born on 25 March 1625 in the parish of St Olave Hart Street, London, to Sir John Harrison of Hertfordshire and Margaret Fanshawe, and had three brothers and a younger sister.
They spent the latter years of the Civil War and the Interregnum travelling, for instance to Caen, Paris, The Hague, Ireland, Madrid, and Flanders, as well as London, Yorkshire, Huntingdonshire, Hertfordshire and Bath.