The Visitor / Tepper, Sheri S

Disme Latimer, born nearly a thousand years after an asteroid destroyed much of civilization, is forced to hide her growing magical powers from her stepsister, an official in the oppressive Regime that runs the planet, while seeking to learn the truth about an ancient text written by her ancestor which suggests that truth and science still survive.

The "magic" that was once America died with most of the Earth's inhabitants when the asteroid crashed into the planet. Bits and pieces of earth's history were collected after the diaster and boxes, books, bags, hard drives and filing cabinets lay sprawled in a heap, molding in darkness. Destiny has chosen Disme Latimer to lead a wasted world out of darkness...with a book. But the book is a sacred, unsettling tome, rife with disturbing ideas and revelations.