 Cosgrave was a member of the Ladies Land League which had been founded to support the actions of the Irish National Land League.She was present at the founding of Inghinidhe na hÉireann on Easter Sunday, 15 April 1900.When Inghinidhe was dissolved and merged into Cumann na mBan in 1914, Cosgrave joined the latter organisation, serving in its Inghinidhe branch until her death.