Hi Tony
For what it's worth here is my conjecture to the spread of the ballad in these islands. Percy was corresponding regularly in the mid 18thc with the Scottish literati who were sending him material, some of it no doubt reworked (i.e., Edward) and it seems reasonable that he would in return send back some of his scarcer material, including our ballad here from the Folio Ms. A reworked version turns up 1818 in the Glenbuchat and a fragment sent to Scott. Ballad-broker David Laing may have had something to do with the dissemination as he did a lot of travelling about between remote communities like Glenbuchat. About the same time one of the literati decided to tag the penance verses onto Cruel Mother and this was taken to new heights later by known ballad redactor Peter Buchan. The story of the ballad would easily then pass from there into Ireland along with the bulk of the other Child ballads found in Ireland. I'm happy to moderate any of this conjecture if anyone can come up with evidence to dispute it.