After the Eclipse by Fran Doricott
Even though sixteen years have passed, Cassie has never gotten over the disappearance of her younger sister. Olive ran off while they were watching a solar eclipse in their grandmother's hometown and was never seen or heard from again. Now an investigative journalist, Cassie returns to the small town to care for her Alzheimer's-stricken grandmother. But another eclipse is coming up, and another girl has disappeared. Cassie knows in her heart that the two must be connected, but will anyone believe her when the evidence doesn't seem to agree?