It would almost be a thesis subject in contemporary History : "Women, Resistance and Pants : war and image of virility"...
In the western movements of Resistance (France, Belgium, Holland - Norway ? Danmark ?), very few women were authorised (by men) to fight openly with weapons. They were usually considered as good and useful dispatchers, messengers or spies, but absolutely not as direct fighters. Wearing pants - and weapons - was generally not admitted in the eyes of most men, and women too, at that time, especially in right-wing or conservative movements of Resistance. Women were generally - and legally in France, up to 1965 - considered as "minors" (like children), not equal, but under the responsability of a man.
It was very different in the left-wing movements of Resistance, mainly Communist ones, in Italy, Poland, Soviet Union or Yougoslavia. Men considered women as sisters of arms, real and competent she-warriors. They often had a free choice to wear what they wanted to fight and die. Equal rights - facing the enemy, facing the death - were a reality in Communist movements during the war.
For the Spanish "milicianas", overalls and pants were common in the Anarchist and Communist movements. Rape was part of Franco's terror tactics : it was better for women to cover the tracks (ie. not to be easily identified as preys).