I can ask my native speaker friend. I also think French uses the singular where we would use the plural, but my guess without actually knowing French is that it would be more in a "women are X" context, speaking of women as a collective, and not in an indeterminate subset of women. Especially since there is a specific woman in the context of this letter. But I may have to eat my words soon! I've already had to eat humble pie around my "putains" French fail. (Go Selena.)