I wonder if the original Raeliana was deliberately looking for a way to displace her soul for some reason (maybe to escape her doomed engagement?) and ended up in the body of the blonde protagonist girl? And that's why she's been acting against the script of the novel. It might also explain why she's trying to get the current Raeliana killed, if she's been having similar soul/body problems. Maybe she was banking on her original body being murdered by the old fiance, which should have severed her connection to it, but now that the new Raeliana has survived, the old Raeliana is having to make sure she dies anyway?
Though, that doesn't account for her murder as Eunha, in her original world. I assume they're maintaining the mystery around that for a reason. Seems like it has something to do with the Black Vestal and mysterious Catholic (lol) soul magic?