A Blightress of Wrath (Conduit of Light Trilogy #3) by Chelsey Tompkins:
 
The past is set. The damage is done. War against the Blightress rages. 

As Saelyn finally leaves the protection of Felgren Forest, she must decide what risks she is willing to take in saving her father. More powerful than she admits, Saelyn will confront the cruelty of war with the help of Thevin, her best friend and man she secretly loves. And as the truth of her mother's past is revealed, Saelyn begins to understand her role in ending the fight against the Blightress of Wrath. 

Don't miss the final book that completes the stories of Karus, Revich, Saelyn, Thevin, and the Blightress who haunts them.