There is indeed an older song in Irish called "Bean an fhir rua" ("The red-haired man's wife"). Hugh Shields discusses it briefly in "Narrative Singing in Ireland". He interprets it simply as referring to the love of a woman before she married someone else.He would be well aware of the allegorical possibilities.

I don't remember the Irish words or their literal meaning but will look into it when I get a chance.

Regards