She knew the girl ... woman... would be at Hogwarts. All she needed to do was Apparate to Hogsmeade and walk over. Narcissa knew it was that easy, yet something stopped her. She instead kept wandering through London as though it were perfectly natural for her, despite her hand hovering near the muggle weapon. It was non-lethal, and held zero magical resonance, so the Ministry wouldn't be able to trace it back to her.