Whisper Falls Series by Elizabeth Langston

While training for a mountain bike race, high-school senior Mark Lewis spots a mysterious girl dressed in odd clothing, standing behind a waterfall in the woods near his North Carolina home. When she comments on the strange machine that he rides, he suspects something isn’t right. When Susanna claims to be an indentured servant from 1796, he wonders if she's crazy. Yet he feels compelled to find out more... moreWhile training for a mountain bike race, high-school senior Mark Lewis spots a mysterious girl dressed in odd clothing, standing behind a waterfall in the woods near his North Carolina home. When she comments on the strange machine that he rides, he suspects something isn’t right. When Susanna claims to be an indentured servant from 1796, he wonders if she's crazy. Yet he feels compelled to find out more. Mark enters a ‘long-distance’ relationship with Susanna through the shimmering--and temperamental--barrier of Whisper Falls. Curious about her world, Mark combs through history to learn about the brutal life she's trapped in. But knowledge can be dangerous. Soon he must choose between the risk of changing history or dooming the girl he can't stop thinking about to a lifetime of misery. less

I have never been useless in my life. Rescued from a life of servitude by the boy she loves, Susanna Marsh escapes across two centuries, only to be plunged into a world she's ill-prepared to face. Unable to work or go to school, Susanna finds herself dependent on others to survive. Immersed in the fun and demands of his senior year of high school, Mark Lewis longs to share his world with the girl who's captured his heart... moreI have never been useless in my life. Rescued from a life of servitude by the boy she loves, Susanna Marsh escapes across two centuries, only to be plunged into a world she's ill-prepared to face. Unable to work or go to school, Susanna finds herself dependent on others to survive. Immersed in the fun and demands of his senior year of high school, Mark Lewis longs to share his world with the girl who's captured his heart. But first he must tackle government bureaucracy to prove Susanna's identity. Overwhelmed by her new home, Susanna seeks refuge in history and in news of the people she left behind. But when she learns that danger stalks her sister, Susanna must weigh whether to risk her own future in order to save Phoebe's happiness. less

...that's not freedom at all. With the dangers of the past behind them, Mark and Susanna are reaching for what the future holds. As Mark's final year of high school draws to a close, his focus shifts to choosing a college and moving on. For Susanna, it's time to set down roots and realize dreams of her own. Yet the whispers from the past continue. A glimmer in the waterfall reveals messages from a dear, old friend... more...that's not freedom at all. With the dangers of the past behind them, Mark and Susanna are reaching for what the future holds. As Mark's final year of high school draws to a close, his focus shifts to choosing a college and moving on. For Susanna, it's time to set down roots and realize dreams of her own. Yet the whispers from the past continue. A glimmer in the waterfall reveals messages from a dear, old friend. As she fights to resist their call, Susanna must finally confront the consequences that her choices have made across two centuries. less