She is credited with contriving the acquittal of her husband, the zealous but unsuccessful conspirator John Mordaunt, for treason in 1658, and she acted as an intelligencer for the royalist network in 1659.

During one of her stays with her mother in 1656/7, Louise, Princess Palatine, the Queen’s daughter, painted her in the character of the nymph Pomona and another portrait, which was given to Mary Evelyn at her request.

Fellow royalist Edward Hyde described her shortly after the marriage as 'a young beautiful lady, of a very loyal spirit, and notable vivacity of wit and humour, who concurred with him [John] in all honourable dedication of himself.

[8] A major test of her commitment came in April 1658 when John was arrested for conspiring to raise troops for Charles II as part of the future king’s 'Great Trust and Commission.'

Remaining in Calais alone, she began the main phase of her role as a Royalist intelligencer, passing encrypted letters between her husband, the king, and other conspirators, with the support of the Queen of Bohemia.

[16] Elizabeth had to deal with John’s continued troubles, including his impeachment after an accusation of false imprisonment and attempted rape in 1666 and a property dispute with his brother in 1672–4.

[17] In July 1674 their house and goods were seized, and she was only able to pay the household debts when she received delayed payments from the Exchequer after John’s death in 1675.

From 1656/7 she kept a private devotional diary, where she recorded her reactions to everything from disagreements with her mother-in-law and concern over her children’s illnesses, to her feelings on the Restoration of the Monarchy.