You know, it occurs to me now, having read other people's comments and calmed down a little, that she didn't say what sort of incest porn. If it was father/daughter, then I'd be just as upset in her place, whether or not he actually has sexual feelings for his own daughter. But it's possible that he's reading or watching, I don't know, brother/brother, and that she's generalised from that to "he must like incest in general!"? In which scenario I would say that it's none of her business.

But yeah, what you said about underaged porn actors. There's no way to make that right.