""Congratulations on the resurrection of your life," a colleague wrote to Emily Rapp Black when she announced the birth of her second child. The line made Emily pause. Her first child, a boy named Ronan, had died before he turned three years old from Tay-Sachs disease, an experience she wrote about in her first book, The Still Point of the Turning World. Since that time her life had changed utterly: She had left the marriage that fractured under the...