Guardian

"If you could save just one person, would you? Or would you stand aside and watch as they were killed, knowing you could have stopped it?"
"I would save them, it would be wrong to stand aside and let that happen."
"Okay, now if you could save a whole population of people, would you? Even if it meant you'd have to give up your life as you know it, you'd have to become a completly different person, give up on the people that are in your life, and give up on the people you loved, would you? Sacrifice yourself, to save billions of people."
Alexa Gray never thought she'd be able to survive high school. And she was right to think that. She dies, but doesn't leave the world to miss her. No, she comes back, with more power then ever. She's a guardian angel now, and the fate of the world lands on her. She must chose between her life, and the life of the entire human race.