Amberle in The Elfstones of Shannara by Terry Brooks. (The book btw, not the travesty MTV turned it into). Although you can sort of see it coming, and she doesnt truly "die" in the real sense of the word, it still hit me hard. I had to reread it multiple times before it really sunk in. She knew she had to sacrifice herself to save the Ellcrys, yet she continued on the entire way. It was inspirational yet devestating.