Her brother, Joseph, was a signatory of the 1916 Proclamation, and Dillon actively supported his involvement with the Irish Volunteers and the Irish Republican Brotherhood. She helped to smuggle gelignite and ammunition into Dublin by taking delivery of the two bags in February 1914 from Liam Mellowes. She was a friend of Michael Collins, who she met through Joseph in 1915 to help her when she had been left to manage the family finances and property while her mother was visiting the United States. In 1916, Dillon was living with Joseph at Larkfield House in Kimmage, the grounds of which were used as an Irish Volunteers training camp. In the run up to Easter 1916, the house was home to large number of Volunteers who came from London, Liverpool, and Glasgow. Joseph gave her a pistol, which she carried continuously in her jacket.