Strangulation might be unlikely because her hyoid bone was intact, although it is POSSIBLE to not break it... I am leaning towards a scuffle / fall /suffocation from hands over mouth and nose to make her be quiet
IMO her death was not a single event. It's possible she was knocked unconscious (chipped tooth) out the back patio by punch(s) to the face/mouth area which bled. She was dragged by the feet to the car, possibly placed in some kind of tarp to protect the upholstery.
She may have regained consciousness, tried to escape or escaped, was chased & cornered hence screams & muffled screams heard elsewhere, then murdered.
I tend towards suffocation/strong hands over mouth and pinching nose simultaneously. Both of her murderers hands/arms needed to be engaged for her to reach up and scratch him on face, neck and chest IMO. She only had a few minutes to inflict damage on her murderer.
She was taken under the bridge, transported in a tarp, possibly by two people, one holding the head area and one holding the feet area, then rolled out of the tarp down the embankment. He (they) had to be quiet and quick to avoid risk of being seen/heard that night.
Satisfied that he (they) had successfully disposed of her body, they did not think/did not see her blood in the vehicle when the back seats were uprighted again and the boxes of toys placed in the back of the vehicle.
Thank you to QLD Police for their prompt response, especially Cons. Keiron Ash for his astute investigation that morning. Thank you to the Detectives for escalating the investigation in the house that morning. Great work IMO.