After the Republic's defeat, she went into exile in France, where she supported the French Resistance, Spanish Maquis and eventually ETA.

She grew up in the Donostia neighbourhood of Egia [eu], where she learned to read and write at the Atocha public school.

[3] Her intense participation in the Revolution of 1934 led to her being arrested and sentenced by a military tribunal to nine years in prison for distributing propaganda and twenty more for possession of explosives.

[1][2][3] Shortly after her release from prison, she met the anarchist militant Felix Likiniano, who was to become her lifelong companion, and became sympathetic to the Mujeres Libres group, created the same year, although she did not become a member.

[3] After the outbreak of the Spanish Civil War in July 1936, she joined an anti-Francoist militia, taking part in the defence of Donostia and the battle of Irun.

[4] In 2022 the documentary Casilda, el eco de otros pasos, by director Juan Felipe, deals with the figure of Hernáez.