The Petulant Princess by M.A. Frick

What if you never wanted to be the princess of the story?

At the tender age of six, Elspeth’s father, King of Wynterborne, died—leaving her without parents. Her older brother, Adastrus, was her remaining guardian. Unfortunately, he was also mad.
Sainte Nytestorm was her salvation, and fifteen years later may be her end.
Growing up in a kingdom that was not her own, Elspeth made it by. She scrounged and fought for everything she had—which wasn’t much—but with her friends, it was enough. Nearing her twenty-first birthday, Sainte appears and drags her away from the only real home she’s known.
To remove her brother from power, she must pass the Trials of the Gods. But where were the gods when her brother tried to kill her? Relying on the whims of gods that no one can see is a death sentence. Elspeth is thrown into the sea of politics.
And she can’t swim.
The lost princess, once thought dead, is restored. The brother, reigning regent, is eager for her death. The gods are watching, moving behind the scenes, playing their games.

For Elspeth, it’s too much. She has everyone, but only wants Sainte.
For Sainte, it’s his duty. He has Elspeth, and needs no one else.