In what sense is this a coincidence? In order to be rationally convinced of an idea, you need to be exposed to the idea. That's not surprising. Now it may be the case that there is some other religion out there, to which she hasn't been properly exposed, that provides more satisfying answers to the questions that motivate her than Catholicism does. But given that she hasn't in fact been exposed to that religion, I don't see how you can blame her (on rational grounds) for not converting to it. I believe in all kinds of scientific theories because they're the most convincing ones I've encountered so far, not because I've evaluated them against every other possible theory.

The choice she made was essentially between atheism and Catholicism (and perhaps a couple of other religions in which she was well schooled), and she decided Catholicism made more sense to her than atheism. You can't blame this on a lack of exposure to atheist arguments, I don't think. She was an atheist blogger (as in, someone who blogs advocating atheism) for a while before converting, and at least somewhat familiar with LW-style rationalism, if I'm not mistaken.

Also, she's not claiming her conversion to Catholicism is the consequence of some mystical experience that had nothing to do with her prior exposure to the religion. If that were the case, I'd understand suspicion that the mystical experience just happened to coincide with the dogma to which she had been exposed. But as far as I can tell, she says she converted to Catholicism precisely because she became immersed in Catholic philosophy and found a lot of it very convincing, so the exposure to Catholicism isn't a coincidence, it's the admitted cause of her conversion.