Final answer:
The second-most prominent Irish saint, potentially linked to the co-opting of a pagan goddess, is Saint Bridget. Her story reflects the blending of Christian and pagan traditions during the spread of Christianity, akin to the transformation of pagan sites into Christian ones as advised by Pope Gregory.
Step-by-step explanation:
Perhaps an opportunistic co-opting of a pagan goddess, the second-most prominent Irish saint is Saint Bridget (Saint Brigid), known for her generosity and Christian deeds. Her legend and sainthood significantly contributed to the spread of Christianity within Ireland, and her tale is intertwined with earlier pagan beliefs, suggesting a form of cultural integration rather than a complete cultural displacement. This approach is reminiscent of early Christian practices elsewhere, as in the case of Pope Gregory advising the consecration of pagan sites for Christian purposes, easing the transition to Christianity by blending rather than entirely replacing pagan traditions.