You might be interested in this thread:

http://giftedissues.davidsongifted.org/BB/ubbthreads.php/topics/180637/1.html

I don't hear "why" often so much as, "How did you know that?" from my DS2.25, and he expects lengthy explanations of how I arrived at a given conclusion. I'd call it reverse-engineering the scientific process. Like 1111's younger son, my DS also will ruminate and then bombard me with a detailed hypothesis about why something is the way it is, and then we discuss it in detail. Maybe your DD has developed her own more efficient hacks for getting at the information she craves.

What is to give light must endure burning.