I keep thinking the only way the Parish found out about this is that she told them. How else would they know? If she truly wanted to attempt IVF... she should have kept her private life... private. By telling the Priest, she essentially painted him into a corner. IMHO.
Maybe she was letting them know so that they could start looking for her replacement while she took maternity leave?
If she told him in confession, he could not have taken any public action without violating the laws of the Church.
If she told him outside of confession that’s a different story. It would be an unusual priest who would fire someone who wasn’t making a public scandal of this, who wasn’t telling a lot of people.