Yep, the style is very Scottish Traveller-like, the open-throated conyach style... But I don't think Annie Cosgrove is a Traveller. Possibly the Mrs McConville from whom she learned the song was an Irish Traveller living and working in the Central Belt of Scotland, which wouldn't be at all surprising given the time period in question.
Of course there has always been a lot of cultural exhange between Ireland and Scotland, a lot of Irish song tunes, etc ending up in Scotland - eg Sheila Stewart's 'The Lakes of Shillin' - and the ABBA form of the rhyme scheme along with the Mixolydian tune screams 'Irish' to me... I wonder whether any Irish Mudcat users might have anything to contribute?