Reddit reviews The Lost Girl

The Lost Girl by Sangu Mandanna

From Amazon -
Eva's life is not her own. She is a creation, an abomination - an echo. Made by the Weavers as a copy of someone else, she is expected to replace a girl named Amarra, her 'other', if she ever died. Eva studies what Amarra does, what she eats, what it's like to kiss her boyfriend, Ray. So when Amarra is killed in a car crash, Eva should be ready. Eva is sent to take her place, knowing that if the deception is discovered it means her death.