We Are All Completely Beside Ourselves by Karen Joy Fowler
Meet the Cooke family: Mother and Dad, brother Lowell, sister Fern, and Rosemary, who begins her story in the middle. She has her reasons. "I was raised with a chimpanzee," she explains. "I tell you Fern was a chimp and already you aren't thinking of her as my sister. But until Fern's expulsion she was my twin, my funhouse mirror, my whirlwind other half and I loved her as a sister." As a child, Rosemary never stopped talking. Then, something happened, and Rosemary wrapped herself in silence.