Ack! Yes, you're right, no passport. Brain fart. If they were traveling with her as a lap baby, they'd have to provide a birth certificate (though now that I'm typing it, it's possible her father had a copy), although they could have purchased a seat and it might not have raised an eyebrow.
I think the chances are very very slim that this was accomplished, though. He was in a frenzy at the time of the killing, I am having a hard time swallowing that he could have have the thought process to do this, and then accomplished all this in secret, and no one has spilled the beans in all these week.