Time's Daughter by Lyra Thorne

She went searching for a memory-and disappeared from her own.After her mother's sudden death, Lissy stumbles across an old tunnel buried deep beneath her hometown. What she doesn't expect is to step out the other side into the middle of the Civil War. With the past unfolding around her and no clear way back, she begins to uncover truths her family never told her-about who she is, where she comes from, and why no one seems to remember she ever existed.Time's Daughter is the final installment in the Threads of Time series. (can be read as a stand alone)