The Merciless Ones by Namina Forna (Deathless #2)

It's been six months since Deka has freed the goddesses and discovered who she really is. There are now wars waging across the kingdom. Otereans now think jatu are traitors to the nation. Deka is called a monster.
But the real battle has only just begun and Deka must lead the charge. Deka is tasked with freeing the rest of the goddesses. Only as she begins to free them, she begins to see a strange symbol everywhere in places of worship and worn on armor. There's something unnatural about that symbol; just looking at it makes Deka lose her senses. Even worse, it seems to repel her powers. She can't command or communicate with the new deathshrieks. In fact, she can't even understand them when they speak.
Deka knows freeing the goddesses is just the beginning. She can tell whatever dark force out is powerful and there is something sinister out there threatening the kingdom connected to that symbol--something merciless--that her army will need to stop before humanity crumbles. But Deka's powers are only getting stronger...and her strongest weapon could be herself.