If it is real, then that’s mega dumb of the person tbh bc it’s literally harassment. However, I still think it’s her writing those messages to herself, though a lot of people in the comments are suggesting it’s someone who know her irl which to be fair could be the case.
That said, if it genuinely is some weird online stalker, going to the police will do absolutely nothing. This is Spain and you can report it but they 100% ain’t gonna do shit unless you can provide them with the persons identity.