Yes, the old, old question as to who would qualify as a superhero(ine). Perhaps as lbsutton has listed Sheena etc., we should use the terms masked mystery women or costumed adventurers. Anyway, can I add:-
Acromaid, who had 1 issue of her own comic in the late '50's
Val Venture, costumed heroine who appeared regularly with Ace Hart in Super Thriller late '50's
Phantom Maid appeared in Super Duper Comics, late '40's. This title also had Power Girl.
Electro Girl also appeared and was cover featured in Super Duper Comics, probably only remembered nowadays as a cameo in League of Extraordinary Gentlemen comic.
Tina was a young girl with no costume and dressed as a young English girl but with super powers. She appeared alongside TNT Tom in Coloured Slick Fun comics, around '49 - '50 ish.
If you also want girls in hoods, masks and robes solving minor crimes and mysteries, there are a few teams, The Silent Three being best known, but there were also, Secret Avengers, Phantom Circle, Grey Ghosts etc.
More recently British comics, or more accurately, British girls' comics, featured The Cat - there are a few different Cats, Starr of Wonderland, Justine, Spring Heeled Jill who was a female version of the Victorian hero, Spring Heeled Jack(son).
There are some non-English language super/masked heroines. Let me know if you need more info.