Well, the topic of this thread hasn't been discussed since page 2, so I thought we might try to shake off this attack of the sillies and get back on topic.
Here again is my picture of the triangular abrasion on her neck.
This picture has had the contrast and hue (colour) changed. Green cancels out red in skin colour, so you can now clearly see the shape of the centre of the abrasion. The edges are very well defined and the piece on the top not so well. This shape is exactly the same as would be caused by having the muzzle of a hand gun pressed hard against the skin.
Now I know we have no other evidence of a gun having been used, so this is only speculation. However, if you look at the shape of the head wound, you can see that it needed to have been caused by a specific object. The baseball bat doesn't match, the flashlight doesn't match. This is because they are curved surfaces, so this would have been reflected in the shape of the dislodged bone.
The handle of a handgun, by handle I'm talking about the magazine -- the part where the bullets are loaded in, which protrudes from the base of the grip. I can picture an IDI holding the muzzle to her neck, using it to both hold her down and threaten her at the same time, but being only a little girl, she probably didn't show the sort of fear we might when faced with a gun. So when she was hurt she may have struggled or cried out, and the gun was just raised and brought down on her head while she was lying on the floor. I believe this is the most likely scenario to both produce the shape of the wound as well as the internal damage to the brain. Because she wasn't propelled any distance (such as being slammed against something) there would be relatively little damage to the opposite side of the brain and the skull because her head was already on a firm surface (the floor) so she did not get an opposing injury.
My gun suggestions gets very little credibility from RDI because it is completely opposed to any theories they have put forward. The Rs (as far as we know) didn't own a gun and really, if they did, it's unlikely they would have used it in this way against their 6yo daughter. On the other hand, an IDI would be very likely to carry a gun and also to threaten a child with it and when that didn't work, use it to bash her over the head.
What a pity there wasn't a forensic specialist in these types of injuries called in, but I guess with the BPD being RDI, they wouldn't have even considered a gun might have been used.