Its probable author was Robert Lambe (1712-1795)
who probably was inspired by Kemion or Kempe Owyne

Its possible that the Kemp--- tunes were a reference to events from
about 1308AD to 1328AD during the reign of Edward II

His wife Queen Isabella spent some time at Bamburg Castle during the troubles
with Robert Bruce,and Robert Lambe might have been alluding to those
times

The ballad technically is a snake-maiden narrative in a class
of Woman in White tales common in Scotland,Germany and Switzerland
where the snaky heroine is a metaphor for the soul of the land