I asked this question or a similar one once, but I can't find it now. I'm trying to locate any given sword and sorcery stories with all-out "villainess" characters, especially (and I'm a broken record about this) ones where the big showdown is between her and the hero himself. Obviously that takes a pretty ruthless hero, so not surprisingly most or even all of the ones I can name are Conan comics.
These are the very few I can name -
Conan # 2
Conan # 12 (The showdown scene is pretty much a "WTF" moment, considering the Comics Code and so on.)
Conan # 32, # 36 and # 38 (Even though the character is more of a schemer than an all-out villainess, so she "gets off lightly.")
Conan the Savage # 2
Savage Sword # 76
Savage Sword # 88