The Oracle Betrayed -- Catherine Fisher

This book reminded me somewhat of The Thief.  (No Gen-like character, unfortunately. But characters like him don't come around every often.)  The setting was an amalgam of ancient Greece and ancient Egypt.  At the same time, it was a different world altogether.  There was a fantasy element, but as in The Thief, it was not a traditional one.  The magics described were those of the gods.

Shy and timid Mirany is given the honor of being the Bearer of the God:

And the scorpions slid and rattled on the polished bronze; they made angry runs and shuffled and their quivering tails stung at one another again and again in a maelstrom of fury.  Tiny drops of venom splashed the bowl.  Mirany walked without raising her eyes, her feet stumbling in potholes, her whole body so tense that she was a mass of concentrated energy, eyes and hands and the gently tipping, balanced bowl.  And for a second the god was in her, and she knew she was a great power, and that she held the hemisphere of the world there, with all its puny, squabbling creatures, lifting some, casting others down, queen of life and death.  And then two of the hateful things scrabbled up opposite sides at once, and she stifled a scream and flipped them back, and was Mirany again, scared witless, inches from death.

Shortly after her ascension, she discovers a conspiracy involving the Speaker of the God and the highest-ranking General in the Two Lands to install a puppet on the throne.  Due to her secret disbelief in the god himself, she's rather surprised when he starts speaking to her.  With the help of a teetering-on-the-edge-of-corruption scribe named Seth and a drunken musician named Oblek, she has to try to ensure that the true Archon will take the throne.