The Kiss of Deception (The Remnant Chronicles) - Mary E. Pearson

It took a while to get going and then it got very interesting.  Princess Lia is running away from her destiny, to marry the prince of another country and to become a pawn in the politics of this post-apocalyptic world.  She thinks she has run away without being caught but she's been found by an assassin and the prince she should marry.

 

Complicated and interesting once it got going.