Men do one kind of magic, women do another. The magic for one is sky based, the other is earth based. The main character (a girl) ends up breaking down the barrier to show that blending the types of magic makes the spells stronger.
The cover of the book was a reddish and gold based color. It showed the main character and a sort of doorway or archway with a man and maybe a second female character.
The person I'm asking for doesn't think it was a young adult novel. It was a run of the mill fantasy book and she thinks the author was a woman. It was published in the 1960s or 1970s.
She said the book is not Terry Pratchett’s “Equal Rites”.