Things don't break on their own a novel

"Twenty-five years ago, a young girl left home to walk to school. Her younger sister soon followed. But one of them arrived, and one of them didn't. Willa's sister's disappearance has defined Willa's life. Everyone thinks her sister is dead, but Willa knows she isn't. Because there are some things that only sisters know about each other--and some bonds only sisters can break. Willa sees fragments of her sister everywhere--the way a woman on the t...