Many years ago I remember reading a short story about (high?) schoolgirl who suspects someone from her school is witch/demon. I remember after the story escalates there is a confrontation between the two where the bad girl calls a slow witted demon downstairs. This scene is vivid in my memory because the good girl is small and the demon is overall huge and has an erection to match. I thought the title was something like “Twyla,” but I’ve never been able to find it.
I believe this is one of those stories I read in a science fiction anthology my father brought home on one of his business trips in the sixties or seventies. Since joining this site yesterday, I’ve had three other questions answered quickly and correctly, and this should be the last and most obscure for now.