Queens of Mist and Madness by Lisette Marshall

“Fae wars don’t end in surrender.”
Emelin has finally found the bindings, the key to her victory. But to use them, she needs one last piece of the puzzle … and the only person who can give her that information is a stubbornly silent Thysandra.
And an uncooperative captive is the least of Em’s problems.
As the Mother prepares to strike, the magical world continues to squabble. Something ominous is plaguing Creon. And Em’s own newfound powers come with a dark side she did not expect, forcing her to decide just how much she’s willing to sacrifice for the fate of the world.
To find allies and gather the forces they need, Em and Creon have no choice but to face the shadows of their pasts. But when disastrous secrets are revealed and the Mother finally deals her devastating blow … will they still have a future?