I'm still looking for a good copy of Sleator's House of Stairs. Also Grinny, which no one seems to remember but me. Amusingly, it hit me like a punch that my husband's main association with Sleator's name is apparently Space Pig. What?!

Have you tried John Bellairs? There's some prime female characters in his early stuff, particularly Rose Rita Pottinger, though I'm also fond of Lewis, his sad, fat, well-read original POV character. Also the amAzing villainess Selenna Izzard, from The House with a Clock in its Walls.