[1] At the outbreak of the First English Civil War in August 1642 George sided with the king and was killed whilst commanding a cavalry regiment at the Battle of Edgehill on 23 October 1642.

She was granted permission by the parliamentary forces to enter London in May 1643 to put her husband's affairs in order and used this trip to convey messages from the king to Royalist sympathisers in the city (part of the Waller plot).

[1] In Summer 1647 Katherine was granted extensive rights and claims over her husband's estate by the House of Lords, perhaps due to the influence of her brother James Howard, 3rd Earl of Suffolk.

Katherine and her husband attempted to free the king but were foiled by Major General Thomas Harrison; though they were able to pass messages from Charles to his wife Henrietta Maria of France.

Katherine's death was a blow to the Royalists and she was described by Edward Hyde, 1st Earl of Clarendon, in his History of the Rebellion as "a woman of a very great wit, and most trusted and conversant in those intrigues which at that time could be best managed and carried on by ladies".