If Raeliana and the blonde girl are connected (they both get sick because of their soul) I think maybe she was supposed to be in the blondes body.
My theory 😂:
We know that Raeliana was visiting a witch before the FL took her body.
Maybe she knew about her fate and what was about to happen, and so she decided she preferred the blodes destiny.
She then manages to put her soul in the blonde, but her body is vacant and the FL's soul had to come anyway... So the FL takes Raeliana's body.
The real Raeliana in the blondes body then wants to continue the original plot and that's why she keeps trying to kill the FL and get closer to the Duke. Also, she killed the witch to leave no traces.
Obviously, since the "roles" are the bodies, the blonde is his fated partner, but the one that was supposed to fulfill that "role" was the FL!
I can't wait to see if I'm right or if there will be an amazing plot twist! 😍