Except one thing kept bothering her: the toilet, specifically the toilet seat.
Because here is how the L household looks like:
Now little PJ was very scientifically savvy and knew that since she and mommy were both females they need to sit down on the toilet. On the other hand since daddy and little bro were males they didn't need to sit down (though the actual mechanics were never ever witnessed.)
Using her advance math powers little PJ discovered:
With that discover, little PJ then observed this constant trend:
That blew her mind.