The War Between the Hearts by Nann Dunne

Intent on serving the Union Army as a spy, Sarah-Bren Coulter disguises herself as a man and becomes a courier-scout for the Confederate Army. Soon the savagery of war shakes her to the core. She stifles her emotions so she can bear the guilt of sending men, and sometimes boys, into paths of destruction.

When Sarah is wounded and in danger of dying, her life is saved by a woman who stirs desire in Sarah for the first time. But Faith Pruitt is Sarah's enemy and betrays her into a hell worse than Sarah has ever known. Sometimes hearts are killed instead of bodies.

Can Faith save Sarah's heart and awaken her to love? Do they even want to try? Or are the women destined to be at war with each other forever?