Malcolm, I'd put my money on her having obtained it from A.L. Lloyd. In his essay on Briggs, Harper quotes Carthy as saying that Lloyd gave him the odd song, but that he'd would send 'a load' to Briggs and to the Watersons. Briggs refuted the idea of Lloyd as her 'mentor', but is quoted by Harper as saying: 'But having said that he was tremendously generous in sharing work and his knowledge of songs with me. All he would say is "I've found this song, have a look, see what you think". That was all'.

--Stewie.