I don't know where I got the impression that the tune was a borrowed traditional one; it certainly doesn't say that on the site I indicated. My mistake.

The song seems to have been recorded by several "Celtic" acts; you can hear "Celtic Soul" playing it at (amongst other places) Paddy Reilly's Radio Links, where it is implied that the song is traditional, and Irish.

Nancy McAllion herself can be heard singing it, in a brief excerpt from Women Of The World - Celtic at CDNow