Single Sundays: Juliet by Anne Fortier

Synopsis (from Goodreads.com):
Twenty-five-year-old Julie Jacobs is heartbroken over the death of her beloved Aunt Rose. But the shock goes even deeper when she learns that the woman who has been like a mother to her has left her entire estate to Julie’s twin sister. The only thing Julie receives is a key—one carried by her mother on the day she herself died—to a safety-deposit box in Siena, Italy.