Just found this so it looks like Ystrad in Ystradyfodwg, this would make sense as the parish church is within that area, also if I remember rightly, as it was a while ago, her parents Robert and family were in Ystrad on census.
The English translation of the Welsh word Ystrad can be taken as meaning Vale, a flat space or valley bed. It is thought that Ystrad itself takes its name from the old parish name of Ystradyfodwg, or Vale of Tyfodwg, Tyfodwg being thought to have been a disciple of St.Illtud. Historically, the area known as Ystrad has had a number of different names. Early records call the area Ynys Fach, which can be translated as, ‘a low lying meadowland near a river', and subsequently early Ordnance Survey maps call the area Heol Fach
Do you have Dianas' birth cert, what was address? If it was Trealaw and Lot died, he would be buried there?
Cas