Well, I found a brief mention of the song at www.horsebrass.com, which is the website of a Real Ale pub in Portland, Oregon (!); somebody has quoted a Welsh song which may or may not have anything to do with it (I can't tell, 'cos it's in Welsh), but does mention Jenny Jones and Llangollen, where apparantly there is a pub that bears her name:

Re: The Mystery of the Jenny Jones Pub, Wales

Malcolm