Richie,
here's a sound recording of Kathleen Behan's version, as recorded by Hamish Henderson:
https://soundcloud.com/user-860765554/kathleen-behan-my-bonny-brown-boy

Here are the booklet notes, but they tell us nothing about the singer, unfortunately.

From "Hamish Henderson Collects Vol. 1" (2005):

15. MY BONNY BROWN BOY SF1956/1(A1). Roud 10. Child 12
Greig/Duncan 209. Kathleen Behan, Crumlin, Dublin. 1956.

Professor Child called this Lord Randal and gives over a dozen examples. Attempts have been made in the past to try to tie this ballad to an actual event, usually to the family of Ranulf, sixth Earl of Chester (d. 1232), but as it is known in one form or other all over Europe (Italian sets are known from c. 1630) this has never been successful. Hamish Henderson believed that this ballad, 'like many Child ballads found in Ireland', was originally from Scotland.