Unfortunately, Ms McKennitt doesn't always say where she gets her material. In this case, she seems to have learned it from a Mary Black record ("Harking" was Mary's mis-hearing of "Buchan"). Mary learned the song from Nic Jones (perhaps via her brother Shay) and said so: there is really no excuse for McKennitt's failure to acknowledge the fact that, in the form she recorded it, the song is partly of Nic's making.

Nic adapted the tune from Christie, with a text collated and slightly re-written by himself from the examples in Child. Christie's tune is the only example in Bronson; Bronson comments that the second strain seems (as so often) to be of Christie's own making rather than authentically traditional. Since then, two further examples with music have come to light (John Mowat and John Rae in the list above) but I don't know if they resemble Christie's.

The other text above is Child's example A.

It's unlikely that there is much to say in this new thread that can't already be found here in previous discussions (see the list of links now added at the top of the page). I'll just add Christie's comment, with the warning that Child considered that there was very little evidence to support the suggestion.

"The above beautiful air was arranged by the Editor and his father from the singing of two aged relatives. Through one of these relatives, and her 'forebears,' the Editor can trace the accompanying Ballad almost up to the marriage of George fourteenth Baron Saltoun to Helen, daughter of John Gordon, Esq. of Kinnellar in 1756; but cannot trace the change of 'Helen' into 'Jeanie' in the Ballad. The first verse given here seems to prove that 'Gordon of Annachie' in Buchan is referred to, instead of 'Gordon of Auchanachie' in Strathbogie."

-W Christie, Traditional Ballad Airs, Edinburgh: Edmonston & Douglas, 1876. I, 10-11.

See also appendix to vol I (p 287), where Christie adds:

"In the year 1781, Garden of Troup was the owner of the Manor of Annachie, in the Parish of Deer in Buchan, Aberdeenshire. See 'Collections for a History of the Shires of Aberdeen and Banff,' p. 398 (Spalding Club Edition). Before writing the note, p. 10, the Editor was led to believe that in 1740 a Gordon was owner of Annachie. This, so far, he has been unable to authenticate."

All this doesn't mean that the incidents described in the ballad ever took place; just that the names belong to real families and places. I don't know why anyone would imagine this song, specifically set in Aberdeenshire, might be in some way Irish; unless they have only heard it from Mary Black's arrangement and just made an assumption based on her accent.