Growing up,Eva has 2 companions a girl her age, and a grown woman, that no one else can see. Her Mom died right after she is born, and she experiences a certain degree of loneliness, and is less than successful forming friendships at school. The companions meddle in her life, sometimes to Eva’s delight, sometimes to her disappointment.
It is Never clear whether the ghosts are real, or a figment of Eva’s imagination, because the ghosts don’t always behave well. It could be that Eva blames her bad behavior on these ghosts, which are nothing more than a figment of her imagination. But I lean to the other possibility, that they really are present. But you can see where either narrative makes sense.