If by “rationalist”, the LW community means someone who believes it is possible and desirable to make at least the most important judgements solely by the use of reason operating on empirically demonstrable facts, then I am an ex-rationalist. My “intellectual stew” had simmered into it several forms of formal logic, applied math, and seasoned with a BS in Computer Science at age 23.
By age 28 or so, I concluded that most of the really important things in life were not amenable to this approach, and that the type of thinking I had learned was useful for earning a living, but was woefully inadequate for other purposes.
At age 50, I am still refining the way I think. I come to LW to lurk, learn, and (occasionally) quibble.
WRT to de-Catholicising your mother: it has been rightly said that Catholicism is the most rational and consistent of all the religions. So, it would be a pity if you dissuaded her from Catholicism and inadvertently landed her in a less rational religion!