JA was talking of one thing, and now of another.

In the former she criticized those who made fun of novels, even authors of novels seemed apologetic about it, and people in general tried to pass off as superior beings (eg, JT) by saying they didn't read them.

IMO here she is parodying readers who, on the other hand read gothic novels and forget the reality. JA contrasts the two readers Henry Tilney and Catherine. The former enjoys it and the latter is getting into a frenzy about murdered/imprisoned wife.

In 'Udolpho' she had read about Montoni (a character like the General to some extent) who had imprisoned his wife. In the same book there was another incident of a marquis poisoning and murdering his wife. The colour of her corpse changes to black, a clear sign of poisoning of some known sort. The matter was hushed up, and he was never caught - and Catherine was not going to let this happen in this case ;-)

I also think that this scenario has been shown to indidcate that what happened in gothic novels could happen elsewhere where the murderers were not caught, but could not happen in England.
I think she is writing with a patriotic heart here.