Mortina e l'odioso cugino (Mortina #2) by Barbara Cantini
Mortina and her best friend, an albino greyhound named Mesto, live with Aunt Dipartita and spend their days playing with the ghosts of Villa Decadent. One day, however, something unexpected happens: some village children, friends of Mortina, arrive at the villa after receiving a mysterious invitation, while Aunt Dipartita disappears into thin air. Will the odious cousin Dilbert, who has just come to visit her, have anything to do with it?