I don't have a best theory yet, but the dog being found where it was points me more toward thinking that someone wanted to make sure it was cared for, so that could support your best theory. Or she's being held hostage in the building and her vehicle has been hidden or dismantled. (That's a wild theory, but it does fit the few facts we have.) I'd jump on the 'got in her head and fled' theory if it were not for her son, and you're right about finding the RR. If HP was without her phone, purse, and vehicle when she went missing, I would jump to foul play almost immediately, but I can't go there yet. JMHO