The Chosen One by Carol Lynch Williams

Kyra has been chosen. She's been chosen to marry her sixty-year-old uncle who is an apostle: the Prophet has spoken. In the world of The Chosen Ones, girls must "obey," get married when they are 13, and NEVER question the Prophet. If they do, bad things happen. 

Williams uses the voice of a thirteen-year-old girl, Kyra Lee, to provide a window into the lives of The Chosen Ones, polygamy, and how one man, The Prophet, uses "God's will" to control, manipulate, and kill