I haven't been able to get fully caught up yet, but I am still of the opinion that the missing link lies somewhere in Idaho.
The residents of the address which 'BST' gave on her SS application, it turned out, regularly took in wayward people and seemed to be somewhat of a hostel. I don't think she just picked that address out of the blue, I think she really stayed there at some point.
Whether she had ever heard of BST when she arrived there is anyone's guess - but my thoughts are:
If she had already known she was going to become BST, she probably went to Idaho from Washington - it might make sense that someone would advise her to go to a different state from where the real BST's death record was. Otherwise, why go to Idaho?
If she hadn't already known anything about BST, then she could very well have been using her real identity when she first arrived in Idaho. I'm kind of leaning toward this thought because it didn't really seem like she had tried to alter her appearance or anything at that point. It seems like her scheme was just beginning...
Or, less likely, she could have lived in Idaho all along, and known about the hostel just because it was nearby.
I also wonder how she was getting around. Hitchhiking? Bus? Did she have a companion with a car at that point that she was traveling with?