The Lost God by Sheila Masterson

Two kingdoms vying for an ancient power. One witch on the verge of releasing it. But all magic requires an exchange.

Memory Witch, Cecilia, is used to sacrificing for power. She’s exchanged her blood for memories, her pride for respect at court, and her forbidden and unrequited love for her guardian, Rainer, for the sake of her duty. It will all be worth it if she can complete the Gauntlet and release the power of the Lost God.
But when the god of war attacks, sending the two kingdoms from simmering tension to open war, Cecilia and Rainer set out on one final perilous journey. They venture deeper into enemy territory than ever before, aided by a charming hunter who offers Cecilia a glimpse of the adventure and romance she’s always wanted.
As the trio encounters vicious memory-stealing hunters, enchanted illusion forests, and meddling gods who speak in riddles, they draw ever closer to the pinnacle of the Gauntlet, and the sacrifice that Cecilia has been dreading. When faced with the most important magical exchange of her life, Cecilia must choose between her kingdom, and her heart, knowing one will be left irreparably broken.