Apologies to Philippa for my level of ignorance in regards threads and links.

Cailín Deas Crúite na Bó is about a woman seen by a priest when called to administer the last sacrament to a dying man. The woman is understood to be a devil who appears in the form of a beautiful woman to tempt priests. In this case, the priest is said to have realised the situation before his vows of celibacy were compromised but she is said to have delayed him long enough that the dying man passed away before receiving final unction.   The song was one of the "amhráin choiscthe" which people did not really sing. It has seemingly been "revived" without the context. I know of situations where even playing the melody of the song by a musician as a slow-air was frowned upon in a Gaeltacht area.

BTW, this particular devil is called the cuaifearnach.