I still firmly believe one individual was responsible for Allison's murder, most likely from an unexpected or accidental escalation of an initial fight/attack. They have probably then panicked, and had a limited window of time to dispose of her body, maybe just trying to do this before daylight.
If she was attacked in the Brookfield area, there are only 4 ways to leave Brookfield which aren't densely populated - and Moggill / Mt Crosby Road is one of those. Having chosen to head that direction, driving along Mt Crosby the area where Allison has been found is one of the first very sparsely populated sections - if you were in a hurry this would be a potential first place to get off the road and try to hide her body.
Sighting of vehicles that moved between where Allison was last seen and where she was found is going to be key - I believe there is not a chance on earth she walked there or did herself harm.
On the depression angle, she was looking after herself, taking regular walks for exercise, maintaining a healthy and busy schedule with her children - not the signs of anyone having major problems with the black dog.
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On a separate note, I don't understand the situation when she was reported missing. It appears now reliably reported (maybe, info on news channels haven't been too accurate throughout) her husband was the last person to see her, watching TV, at 10pm, before he went to bed. This tallies with people questionong how he could sleep if she was missing - according to the current info he didn't know she had gone missing.
So, when he awoke, Allison was gone, and the information so far indicates he assumed she had gone for her regular morning walk. When she 'failed to return' he called police. If I understand correctly, she would be due to arrive home at around 7am. So why would her being only 30 mins late be seen as important enough to call police at 7.30 am? Would it not be more likely she had stopped for a chat? Or be walking slower than usual, or left a bit late? To me, calling police is the ultimate escalation of an issue, and having gone to that extent - posters, driving the neighbourhood etc would be the next thing to do. There was apparently calls or text messages to friends and parents - but when? After reporting her missing on Fri morning or before ? Because again seems weird to worry people around 7am if Allison is due home any minute? The texts and calls most likely didn't happen after 0730 as the police were onsite interviewing / impounding cars / declaring crime scene.
Perhaps the whole thing makes sense if more is known about what other information was given to police as to why the husband would be so concerned so early in the day.