List of Golden Age superheroines.

[paw broon]

Not sure if you'll allow this one?  Enigma was a character in a short series of French landscape comics, around 1947.  The trick with this one was the "hero" is a character in a suit, collar and tie, sporting a domino mask, but, it's actually a young woman, Germaine de Vetheuil who takes the male i/d to fight crime.
https://fr.shopping.rakuten.com/offer/buy/452817327/la-clinique-du-docteur-kolaf-de-collectif.html
Some of you will know of the Spanish pulp series, El Encapuchado and in those novels, there were 2 other masked, costumed heroines, La Antorcha and Mascara Negra, around the mid to late '40's
https://www.tebeosfera.com/sagas/mascara_negra_1947_l._hipkiss.html
The main character El Encapuchado featured in a later series of comicbooks which you can find on CB+.

[hufflepuffle]

Out of curiosity, I decided to build a list of Golden Age female superheroes and this is the list so far. Feel free to point out anyone I missed:

Jane Arden (female reporter in newspaper comic strip) 1928 & later in comic books?
Sally the Sleuth (female detective cartoon in Donenfeld's detective pulps) 1934 & later in comic books?

Maybe they're just platinum age heroines?  ¯\_(ツ)_/¯