I have been searching high and low for this book based on what I remember about it. I remember reading it as a kid so that would have been around the late 90s but may have been published earlier because I got a lot of my books from second-hand stores.
I believe the antagonist is a young adult male who is kicked out of school for breaking into a forbidden library. The once scene I remember clearly is that he is standing on a hill looking down at a valley before descending into it and conquering it using demons as his weapon.
I think the protagonist is a young woman who wasn't formally trained with magic but may have natural aptitude for it, and the book has something to do with the wind. I believe it also had a green jacket with a creature's face on it... I know it's not a lot to go on so thanks in advance.
Books I already tried:
Name of the Wind - published to late to be the right one
Wizard of the Winds - the book I am looking for is definitely European flavor, not middle east.