You can easily find Tirpenry Street by using Google Maps and just typing in the name of the road. It is about 150 metres south-east of Morriston Cross heading towards the River Tawe on Clase Road (A48), and at the junction of Tirpenry Street and Clase Road you will see Seion Newydd Chapel which is probably where the Sunday School your late grandmother would have attended.
Many Thanks Jeff. I'm not familiar with Swansea, and thought that Tyrpenry/Tirpenry was the name of a district rather than a road.
I gather that there was also a Sunday School in what is now Nixon Terrace as well?
I also thought that my Grandmother Margaret Rees's family were Methodists rather than Baptists... Certainly her father, Evan Rees was Baptised in the Weslyan Methodist Tabernacle Chapel in Morriston in 1836. I have his Baptismal Entry.