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I believe it was a standalone, but possibly 2 books. The main character was a female. The mages in the story exploded when they died unless they were completely drained of power first. They could be drained by making a small cut and then the other mage touching the cut and draining them (to the extent it would kill them). A large portion of the book was main character's training to use magic at a school where thy would basically put up magical shields and duel each other. I believe I read it in late 90's to early 2000.