If this was a crime and it was an internal (family-related) one, it could have happened on Friday night (or whenever Aliayah was actually last seen by anyone outside of the household) which would allow much more time/distance to hide evidence and in fact her body. Obviously, no one has come forward to say they saw her on such-and-such date, and LE is not telling.
I just can't help remembering Marc Klaas saying (in reference to Hassani Campbell) about how difficult it is to find a child, that the world is a huge place and a child's body so small...