Undoubtedly a northern Irish ballad, Molly Bawn, and there are several late 18thc copies in the BL and ITMA.

Are you in a hurry as I was going to suggest to Richie he choose this ballad as his next topic? It was printed in New York.

I can easily list what I have in early copies but your man on this and other NI ballads is John Moulden. He wrote a thesis on them. The only one I've studied in detail is The Streams of Lovely Nancy (Strands of Magilligan).