Dai:The album is "Traditional Songs of Wales - Caneuon Traddodiadol Cymru" on Saydisc Records, CD SDL 406. My favourites are "Miner's Life", which is in English to the great hymn tune "Calon Lan", and "Clywch, Clywch". (There should be circonflex over the "a" in Lan, but the keyboard is configured in English right now). The lyrics to all the songs are included.
If anyone can provide details of Siswsann's other recordings, I would be grateful. As I said, I wasn't able to find any.
Edmund