Eilis joined the Keating Branch of the Gaelic League in 1915. In August of the same year, she joined Cumann na mBan having attended O'Donovan Rossa's funeral. Eilis played Camogie with Nora and Bridget Foley and Effie Taafe.
In 1916 when Eilis and her friend Emily Elliot reported to the GPO, they were told by the sentry that they had enough staff. They were directed to Reis Chambers across in Sackville Street. This was where the Foleys from Killeagh ran their typewriting business, while the wireless school was also located there. The volunteers endeavoured to communicate the Rising with the outside world. This became a template for further rebellions worldwide where it was always the radio and television stations that were captured first.
Eilis got a “céad míle fáilte” here, unlike in the GPO, however, there was no food at Reis Chambers. Eilis went back to the GPO and "with great difficulty we crossed O'Connell Street, as it was a mass of barbed wire and barricades", not to mention the odd stray bullet.
Desmond Fitzgerald, Garret's father, refused Eilis supplies without a written order. Eilis persisted and supplies were eventually granted.
Following their return, Eilis received a request to attend the Four Courts. They eventually got there "after probing our way through high, narrow streets to avoid stray bullets." They were sent to Fr. Matthew Hall to attend to the wounded men and women. As the days wore on the severity and numbers of the injured increased. Eilis also helped out by bringing food to the numerous barricades in Church Street.
In advance of the surrender Eilis moved seriously wounded volunteers to Richmond Hospital. Following the surrender Eilis with some comrades stayed in the church and the following day, escaped by mingling with the congregation.
Michael Collins recruited Eilis to work for the first Dáil. Constance Markievicz, Minister for Labour, "asked me would I like to work in her Department." Eilis gave trojan service to the State.