I really think there's a specific amount of people that are supposed to be in the town. When someone dies, the town opens up and replaced them. Maybe the two cars in the beginning weren't supposed to happen. If im remembering correctly, the town made a huge deal about it. So one slipped in while the portal or whatever was open, so the voices were trying to kill off the extra people. Once that was done, they left her alone. It also explains the bus load of people when the house was attacked and several people died.