Another way to think about it. If this was a spirituality blog and Polly's son had been molested by their priest, would it be inappropriate for her, or us, to wonder whether or not she will some day return to the faith? No. It would be if there was no talk of her son's well-being but that's certainly not the case. And RP was in no way pressuring or pushing her, just wondering.
Polly, I imagine the guilt will take a long time to fade.
Just keep remembering that this happens to people in all sorts of life situations and that she is in every way the one who was wrong -- not him, as you realize, but also not you. No one ever suspects that someone who they love, and who claims to love them, could be capable of such a thing.