Background to Molly Bawn[Bán]/Polly Vaughan/The Fowler/The Shooting of his Dear etc.A.L.Lloyd has a good bit to say about it in Folksong in England; some of his ideas may be a little fanciful (to say the least), but they are still interesting. Here is a (shortened) version:
"[A song] despised by Jamieson (who thought it 'one of the very lowest descriptions of vulgar modern English ballads') and rejected by Child but still much loved by singers in Ireland and the eastern counties of England...[synopsis omitted].It seems clear enough that the story is a come-down relic of the same myth that, long before Ovid's time, became attached to the figures of Cephalus and Procris. Procris, an enthusiastic huntress, had a dog that never failed to catch its quarry and a dart that never missed its mark (she obtained them both from Minos in return for bed-favours). She gave both dog and dart to her husband Cephalus. He went out hunting in the dusk, and Procris, suspecting that he was visiting a mistress, put on a camouflage robe and stole out after him. As she hid in a thicket, the dog detected her, and Cephalus, mistaking her for a deer, cast his unerring dart and killed her. He was banished for her murder and haunted by her ghost.
Several commentators...have identified the girl under the apron as a descendant either of a swan maiden or an enchanted doe...in any case the magical maiden who is a woman by day and a beast by night, and fatally hunted by her brother as like as not, is as familiar a figure in folklore as the swans and other birds flying by night, who are thought to be souls in bird form. So the modern-seeming ballad of Molly-Polly Bawn-Vaughan, that Jamieson thought so paltry, in fact reaches far back beyond the time of classical mythology. The song that the experienced Irish folk song collector, Patrick Joyce, thought 'obviously commemorates a tragedy in real life' turns out to be connected with the fantasies of primitive hunting societies...."
Well, there you are!
Malcolm