The Shadow Girl by Jennifer Archer

Sometimes I forget for an hour or two that she's with me. Sometimes I convince myself that she was only a dream. Or that I'm crazy.

For as long as Lily Winston can remember, she has never been alone. Iris, a shadowy figure who mimics Lily's movements and whispers in her ear, is with her always—but invisible to the rest of the world. Iris is Lily's secret.

But when Lily's father is killed in a tragic accident, his cryptic final words suggest that he and Lily's mother have been keeping secrets of their own. Suddenly, Iris begins pushing Lily more than ever, possessing her thoughts and urging her to put together the pieces of a strange puzzle her father left behind. As she searches for answers, Lily finds herself drawn to Ty Collier, a mysterious new boy in town. Together, Lily and Ty must untangle a web of deception to discover the truth about her family, Iris . . . and Lily's own identity.