It’s clear from the bbc footage that she had a Ring type doorbell with camera. Unless the door was unlocked, she would have had to open it to let him in. Could it be somebody that she knew, a tradesperson or similar, somebody with whom she had a dispute. It will either be a random, unlikely in such a remote area but not unheard of, or somebody that she has had previous dealings with.
I don’t think it could be some sort of fantasist, surely. Why would anybody think that. Still nothing would surprise me in this country these days.
I’m not entirely in tune with her political views but, come what may, she was a frail elderly lady who did not deserve to die in this way after years and years of public service.