My dog had that same red bone. Its made of rubber thats not as hard as a typical KONG brand dog toy. The inside/underside is hollow (ribbed with thin pieces of rubber). It could not have been used to bludgeon anyone, IMO.
Your point that LE should have collected it still stands, though.
Yes! It DEFINITELY should have been collected & tested. When I first saw pics, I thought it was a small hand weight, combined with the description of a rounded object likely making the blow, it seemed a very likely possibility. When I heard it was a doggy bone, that did seem to diminish the likelihood that it was the actual object that was used to hit her head. No matter what, it was a complete dereliction not to process it.