A Real Goddess Would Let Nobody Die

A family of three elite mages has defeated Oscanion, a would-be tyrant mage-emperor who had made himself an enemy of humanity. But, it does not feel like victory to white magic prodigy Menelyn: her adoptive father and sister did not survive Oscanion's suicidal final attack, her inadequate shields failing to protect them. Grieving and ashamed, Menelyn withdraws from the world for a millennium, her vast white mana halting her aging, until troubling signs coax her out of seclusion. Is she able--is she willing--to be what the world needs her to be? — Description from novelcodex.org