Yes it is GGE. There is an Aussie saying "Feed him to the sharks." And it has happened many, many times in Australia, more so with underworld and gangland murders etc. That saying has also become a bit of a colloquialism and when said in jest it simply means, get rid of that idiot, he's a waste of space.
Sharon Edward's body really could be anywhere. There is a lot of bushland surrounding Grafton and Lawrence and she could be out there somewhere in a shallow or not so shallow grave. I'm leaning more to Sharon being dumped in the Clarence River for the obvious reason of a shark attack removing any evidence of her. I don't know if JE owns a boat but even a small tinny would be enough to motor up or down river to dispose of a body.