LOL Yes I believe Catherine and Isabella must have thrown the book across the room --- Henry probably thought it a terrific joke! And in hindsight, of course, it's obvious Jane Austen was having her fun there too ... I suppose the reference would not have been lost to contemporary readers who had indeed read Udolpho - I suppose it would have been like HP-references today.
Though I can't see why people were so in raves about Udolpho ---
I was like 'I slogged through the whole damn book for THIS??' I'd at least expected several victims of murder ...
I'd much rather read HP any day.
"I want you to know that you matter. I want you to know that your lives matter, that your dreams matter." (Barack Obama, 03 June 2020)