A saucer sized puddle is quite a bleed out, especially as the injured person has to remain still to get a puddle, otherwise there.
She actually admitted to being in the search area, and she actually admitted to AS that Gannon's socks and the board came out of her truck. Of course, she avoids the question of who put those things in the truck in the first place.
Prediction: Red truck has Gannon's blood in the cab and in the bed; Gannon's excrement in the truck (hence her pre-splaining about poop), and then there's blood in several locations in the house.
I'm wracking my brain about the possible injury. Blunt force trauma from a board doesn't always make for a lot of blood (unless it was his face). Forensics will be able to say something about whether it was a nosebleed (doubtful unless she hit him in the face - in which case there has to be at least one witness to the circumstances still living).
Sadly, I think we'll find a pattern of routine physical child abuse in this household. Intermittent, perhaps, but still routine.