I made a quick circuit of the house, tried the front and rear doors, and even the door up on the deck that led, presumably, to a kitchen. All were locked.
Locks really weren't an obstacle, but Monica Sells hadn't invited me actually to take a look inside the house, just around it. It's bad juju to go tromping into people's houses uninvited.
One of the reasons vampires, as a rule, do not do it—they have enough trouble just holding themselves together, outside of the Nevernever. It isn't harmful to a human wizard, like me, but it can really impair anything you try to do with magic.
Also, it just isn't polite. Like I said, I'm an old-fashioned sort of guy.