Unfortunately, the most logical choice would have to be the worst possible one. William Wood already knew that the house existed. He'd stepped inside its walls and seen it with his own eyes. His desire to track her down to force her to pay for murdering his younger brother was consuming. He wouldn't rest until he exacted his revenge. She would almost despise the man if she didn't recognize a fellow crazy person suffering in their grief. If the roles were reversed, she would want him dead too. With the sickening knowledge that he was in possession of Draco's tracking spell secrets, it wasn't farfetched to imagine that he was the one keeping a close eye on her as she approached the house.