Dear Child by Romy Hausmann
A woman escapes a windowless cabin in the woods and is hit by a car as she tries to find help. When the ambulance arrives, the woman's daughter identifies her as Lena. Her basic appearance matches a woman who has been missing for fourteen years. Even the scar on her face matches, but when Lena's grieving parents see her at the hospital, they realize that this isn't their daughter.
The first few pages had me worried that this was just another version of Room. Stick with it, because it's not that at all. This is so much else going on here, but it takes a while for that to sink in. The story is told by the woman who escaped the cabin, and the daughter, and Lena's father. The details don't add up at first, but it's always clear which character's head the reader is in and whether it's in the past or the present and the more things start to click together and make sense, the more chilling the story gets. I absolutely loved this one and can't recommend it enough.