I think she was put in the water at the scout camp. Objections to the idea she ended up under the bridge in the flood water because a) the crime was premeditated and he wanted her found or b) it seems too far fetched she ended up where she did given the many other places she may have gone do not sway me.
I don't think GBC "planned" his crime as such, as I've written before I think he fantasised about elements of it, focusing on his problems being solved. Like everything else he has seemed to muck up, he dreams big, details are not important and where he gets tripped up. So someone who doesn't realise ringing the insurance company before the body is identified not only looks bad but is useless, may not realise should she not turn up he will have to wait years for the money. The execution of the fantasy was slap dash and while the main theme has a logic (cheating financially irresponsible husband murders wife for insurance money) the details will not follow that logic, as the consequences and appearances were not considered.
As for where she ended up when she could have got caught up in anything, anywhere. But I think about catching a wave when you body surf, you are carried by the water until you hit the sandy floor, where you slow down until you stop, the water no longer strong enough to carry you. So more likely to be spat up on the shore by the river than caught in something in deep moving water. Plus these things are not an exact science right, so even if in all probability she should have been caught up somewhere or gone into the brisbane river it only takes one random event ... a trolley in the creek, a branch, to change what happens.
Anyway, speculation aside, this is one thing that will be known without too much doubt in the fullness of time.
