The Ghost Inside the Monitor — Margaret J. Anderson

PHANTOM OF THE MONITOR
Something weird is going on in Sarah's father's new computer store. When Sarah looks at her reflection in the monitor, the face she sees isn't hers! It belongs to a younger girl, named Pascale, whose tragic story mysteriously writes itself across Sarah's computer screen. Sarah is fascinated, and then haunted, by Pascale's tale -- because the little girl's ghost has a very real grip on her. Pascale repeatedly propels Sarah back in time (where Sarah is forced to relive adventures from Pascale's life in frontier Oregon) in a desperate attempt to solve the century-old mystery of her disappearance. Can Sarah find a way to bring peace to Pascale's ghost? It's either that or risk being marooned in someone else's past, perhaps for good!