Aside from Gothic objects and images, Jane Austen also uses lots of Gothic plot devices, or events, in her book. Generally, these plot devices are used to make readers laugh, and they represent the ridiculousness of the Gothic novels that Catherine takes seriously – which is ridiculous, on her part.
The trouble with these Gothic plot devices is that they were aimed at readers who read lots of Gothic novels, like Anne Radcliffe's The Mysteries of Udolpho. So how can we go about spotting these events and plot devices? Well, these Gothic events are usually accompanied by really witty commentary from the narrator. Also, these plot devices are usually gigantic clichés. They are lame and ridiculous.
A great example of a Gothic event is Eleanor's engagement to that random rich guy in the very last chapter. That sort of thing happened in a lot of popular Gothic novels, and Northanger Abbey is making fun of it through Eleanor. Another example is the sequence in Chapter 21, where Catherine "discovers" a secret manuscript that turns out to be a laundry list. Catherine's anxious and excited search of her room is a parody of what heroines often did in Gothic novels.