She is a lawful zealot, but even by DnD standards I wouldn't call her "good". "Lawful Neutral" (where "lawful" first and foremost is "under the command of gods") perhaps? On the one hand Elder Scrolls, as a universe, doesn't really support oldschool aligment system with grey moral everwhere, and on the other "Skyrim" as a game is way too narrow on story choices for Celestine to fit.
Otherwise she's great, yeah.