The Shade: Orca Currents (Unabridged‪)‬

Safira doesn't believe in ghosts, but the girl in her cabin at camp was not a living person, so what was she? Her friend Trinity is convinced Safira's seen a ghost and sets out to discover who the ghost girl is. Safira is too busy dealing with her family to help solve the mystery. Safira has never gotten along with her sister, Mya, and now that Mya's pending marriage dominates the family there seems to be no hope for friendship between them. But when Trinity discovers the death of a girl named Myra, Safira starts to wonder if the ghost-girl has an important message about her own sister.