I'm trying to remember the title of a fantasy novel I read years ago.  I remember reading it in paperback format in the early to mid 90's, so I'm guessing it was written in the 80's or 90's.  The protagonist was a female.  I believe she had red hair and lived in a castle.  I know the climactic scene involved her climbing a tower and facing various magical obstacles before facing off with some kind of wizard type character.  I also want to say that fire played some integral part, but I can't remember for sure.  Anyone know this book?