Thanks Jack, have a listen to this recording and you'll hear how she pitched the tune. During the same session she played dance tunes on her fiddle in a higher range and played song melodies in lower pitches, which reinforces your suggestion that it was originally a song melody.

The purposely flattened long note (which I notated as a C natural) is a distinctive aspect of the tune which doesn't feature in the songs mentioned so far.

And thanks for the hint regarding writing repeats more tidily, which I'll do in future.