Humphreys attended Mount Anville Secondary School,[4] where she was head girl and became a fluent Irish speaker.

She joined Cumann na mBan in 1919, aged 20, which organisation was founded in response to the dearth of women at the Sinn Féin Convention of October 1917.

To ministers like Robert Barton, the embryonic republic was protected by a hard shell of army and politicians, but this did not prevent women in the movement being arrested.

[6] The family took the anti-Treaty position during the Civil War and the house on Ailesbury Road was the object of regular raids by Free State forces.

The most significant raid took place on 4 November 1922 when IRA Assistant Chief of Staff Ernie O'Malley was wounded and arrested in a protracted shoot-out with Free State soldiers.

Humphreys played an active part in resisting the raid, though she always denied reports that she was responsible for shooting a Free State soldier who died in the fighting.

[10] Humphreys continued her involvement with Cumann na mBan after the Civil War, contributing significantly to the republican movement throughout the 1920s and 1930s.

[10] Despite her affluent background, Humphreys was active in the socialist republican organisation Saor Éire, serving as the group's co-treasurer from 1931.

Her causes continued to be consistently those of Sinn Féin: anti-EEC, and very strongly Catholic, promoting the Mass on television, all in the Irish language.