Daughter of the Moon Book 1: Luminous

Lena is one of five moon daughters, mortal children of the Moon Goddess, Deanna. Lena's job is to Release the souls of people who have died and become trapped on earth before their energy drains and they can't move to the afterlife. But she's only seventeen and, as an orphan raised in an abbey by thirteen "Aunties", her life is pretty sheltered. She helps make healing tonics at the abbey during the day and thinks about her crush Henry as she frees souls by night. Until the night the darkling attacks.
A creature of mist and bone, the darkling is hunting Lena. Varek, a fierce warrior from the north, arrives just in time but the news he brings sets Lena on a quest to save her sisters and figure out what and who is stalking them before they are turned into the eternal dead.