I just had a crazy idea.... If some ufos were of the 'nuts n bolts' variety and these ufos had human time-travelling occupants on them, then maybe the family were connected to the occupants?? What if, one of the occupants knew that the girl would be getting up, at that particular time and that she'd be going to that particular point in the house, to notice the smoke???
They don't call me Sherlock for nothin!