What occurs to me, and this could apply to any case I suppose, is that a perpetrator would likely be willing to take some measure of risk in involving his or her own property, or that of a family member or associate, or, some other personally traveled turf because he or she would have more control over the environment. Dumping in an unfamiliar location runs the risk of a farmer, or fisherman, or worker, or dog walker/jogger coming across a crime scene or dumping ground.
So if a perpetrator's personality is controlling or domineering, it makes sense to me that he or she would choose a place that maximizes personal control.
I think whoever did this wanted to control Heather and ultimately eliminate her from having influence on the life of the perpetrator. So it follows that the control and personality issues would be reflected in what happened to Heather and where she is now.
I guess this is what I was chasing when I asked what is the simplest answer in the big picture. I think there is a simple logic, if you will, to how the responsible party went about this.