She wasn't sure where the flat was located exactly. Based on the surrounding area of where she landed, she assumed that it was located in one of those dodgy parts of London that one didn't want to be found in after dark. It made sense. Kingsley would've been a high-profile capture. The Dark Lord would've wanted him. If he chose not to surrender his life to serve Lord Voldemort, then his execution would've been a powerful incentive for the others in the regime to fall in line. Hiding in the middle of the Muggles in parts of the city no respecting wizard would be caught dead in might've saved his life.