The report was that the body was badly decomposed so in that case it is highly probable that the clothes came off in the water (snagged on branches maybe). As it was they couldn't even identify the gender initially....
http://www.goldcoastbulletin.com.au...of-chambers-flat/story-fnje8bkv-1227598194005
"Local fishermen alerted police about 5.15pm after discovering the corpse in the river.
Investigators were last night unable to determine the gender of the body, which was badly decomposed."
http://www.skynews.com.au/news/top-stories/2015/11/09/pupils-may-hold-clues-in-qld-murder-probe.html
Here it details her body was found along the same river as where she was last but 30km away. This tells me she was carried by the currents (or whatever the river term is).
https://www.google.com.au/maps/dir/...2a35b2b77f400!2m2!1d153.3326201!2d-27.7960922
Here is a map of the area. Skimming along the Chambers Flat Road and Muchow Road is the Logan River. The river twists and turns a lot (which makes me think her backpack and dress are snagged in reeds somewhere). It comes out to Jacobs Well which is almost where Tia's body is found.
If she was murdered and dumped near where her body was found it would not be as badly decomposed as has been reported...
It doesn't appear she got on a bus otherwise that would have been a big clue (and all buses have cctv). If she met someone I think she would of told people. Something happened that morning that caused her to want to stay elsewhere (I remember reading she had asked a friends who's mother said no).... and I think she went down to the creek and fell in for some reason.
That's just my opinion.