Gum card entitled "Women militia fighters in Spain". From the series "To know the horrors of war is to want peace." Produced by Gum.Inc in Philadelphia, 1938.
Gerda Taro, La sombra de una fotógrafa (2010) by François Maspero
Petals and Bullets (2015) by Mark Derby, Story of New Zealand nurse Dorothy Morris in Spain and elsewhere.
https://www.radionz.co.nz/national/programmes/sunday/audio/201773179/mark-derby-petals-and-bullets
Two collections of biographies in Catalan about Republican women in the Civil War.
There are numerous books in Spanish on the role of women but relatively few in English
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Defying Male Civilization: Women in the Spanish Civil War by Mary Nash. This essential text is not cheap, though you can read sections on Google Books.
Into the Fire: American Women in the Spanish Civil War (2002) Don’t know if this film is available online.