If you're still tuning in, Conny, look here http://www.smo.uhi.ac.uk/~oduibhin/doegen/nicruaidhri.htm
for words and a sound recording (recited, not sung) from Glenlark in the Sperrins. The words are about two-thirds the way down the file, and are headed "LA1216.1, Teideal: Story: Tá mé na mháistir scoile". I'd love to know where your grandmother came from.