Crimson Bound - Rosamund Hodge

When Rachelle was fifteen she was good—apprenticed to her aunt and in training to protect her village from dark magic. But she was also reckless— straying from the forest path in search of a way to free her world from the threat of eternal darkness. After an illicit meeting goes dreadfully wrong, Rachelle is forced to make a terrible choice that binds her to the very evil she had hoped to defeat.