[Executive summary: solve the underlying causes of your problem by becoming Pope]

I think it's a mistake to focus too much on the case of one particular convert to Catholicism simply because you know her personally. To do that is to fall prey to the availability heuristic.

The root cause of your problem with your friend is that the Catholic Church exists as a powerful and influential organisation which continues to promote its weird dogma, polluting Leah's mind along with millions of others. Before investing time and effort trying to flip her back to the side of reason, you should consider whether you could destroy the Church and dam the river of poison at its source. I will now outline a metho