Maybe the intruder made prior visit(s) to scout out the house and gather needed items.
That's true. If someone was really obsessed with this kid it is certainly possible they had the house 'staked out' for a while and may have entered it many times before. I would think they would have to have worn gloves, gotten paper from the pad, 'borrowed' the pen, and she could have died closer to midnight if we push the forensic data. But it is possible.