> Obviously, I need to refrain from making conclusions and stick to presenting evidence, as pointed out by Lighter. That's what I learned :)

It's fun to speculate, so feel free; but keep a clear distinction between what might possibly be and and what is certain or very likely.

It's a possibility that the ballad is a come-down version of a shape-changing myth with the explanation of the white apron added as a rationalisation, and some writers did choose to believe that. But we're now disinclined to believe it.

There is good evidence, in the personal and place names, for a basis in a real incident in Ulster, but that leaves the question of how and when the ghost appearances were added to the story. If the shooting really happened, and the young man was tried, was he acquitted and if so on whose evidence? Or was he hanged, but the girl's ghost appearing in court made a much better story?