That's an interesting theory, and by the way your maps are very impressive. The thing that is still puzzling for me in such a scenario is: where was MB going if she was walking down that hallway away from where CG was going to be held?
Thanks.
It remains to be seen where the class was going to be held. But it was somewhere indoors. So at the moment she passed the doors and entered the halls, it certainly wasn't behind her, and we don't know if she went far enough up/down that main hallway to be heading "away from" the CG class area.
So one possible answer is, the fatal stroll was her going up/down that main hallway to take eqpmt to where the class would be held.
Another might be to the kitchen for some reason. Maybe ice? Water?
It has been suggested that perhaps she had a setup routine. If so, we don't know what it was, but perhaps it included a stroll to somewhere for turning on lights, getting ice, doing this or that.