Here & Then — George Ella Lyon

When Abby finds herself drifting in and out of events from the past, she enlists the help of her best friend, Harper, to figure out what to do. And though Harper is at first reluctant to believe the strange tale Abby tells, she can't ignore the message in her friend's diary. The handwriting is Abby's but the voice belongs to Eliza Hoskins, a Civil War nurse who needs their help -- to save lives!
HERE & THEN, a novel for young readers, is subtitled "A Civil War Time-Travel Tale." (Revised edition published by MotesBooks in 2009 - www.MotesBooks.com)