 In 1641, the Great Irish Rebellion broke out.Lettice, by then a widow in her early sixties, became caught up in it at the end of 1641, when Lettice received an insolent letter from her cousin Henry O'Dempsey, Viscount Clanmalier containing fraudulent orders from King Charles I to surrender Geashill Castle to the O'Dempseys, and leave with her people in a safe convoy provided by them.The letter continued with the threat to burn the castle and town, as well as to massacre all the Protestant inhabitants, should she fail to yield to their demands.