Since the new voice has been added I've noticed she pronounces 'nua' like 'noo' (or at least thats what it sounds like to my anglophone ear.) Is this a dialectal variation or was the 'nooah' pronounciation I learned in school a bit off?
It looks to be a dialectal difference. I learned 'noo-ah' in school also. The sole recording on Forvo pronounces the a: http://forvo.com/word/nua/#ga but on Teanglann only the Ulster speaker does so, with the Munster and Connacht speakers saying 'noo': http://www.teanglann.ie/en/fuaim/nua .
Nua is usable in the same ways as “new”, so it could be a newborn, a new adoptee, a new pupil in a school, etc.