Isabella is one of Austen's most audacious female characters. Her style of speaking matches her character, and she often uses hyperbole. For example, in Volume 1, Chapter 6, Catherine asks her how long she was waiting for her in the Pump-room. Isabella replies:
“Oh! these ten ages at least. I am sure I have been here this half hour. But now, let us go and sit down at the other end of the room, and enjoy ourselves. I have an hundred things to say to you. In the first place, I was so afraid it would rain this morning, just as I wanted to set off; it looked very showery, and that would have thrown me into agonies!
Isabella has not been waiting "ten ages," nor does she have "a hundred things" to say to Catherine. And the prospect of being "thrown [... ]into agonies" by rainfall is quite ridiculous. For the remainder of the story, she terms any good thing "amazing" and uses superlative nicknames like "my dearest" and "sweetest." Her use of hyperbole is significant because it mimics the language of the sentimental heroine. It also stands in contrast to the earnest artlessness with which Catherine speaks. Unlike Catherine, Isabella uses language to deceive people; she tries to conceal her ambitions to marry a rich man and rarely means what she says.
Austen uses visual imagery to give the reader a sense of the grandeur of Northanger Abbey. In Volume 2, Chapter 7, General Tilney describes his estate:
The house stands among fine meadows facing the south-east, with an excellent kitchen-garden in the same aspect; the walls surrounding which I built and stocked myself about ten years ago, for the benefit of my son. It is a family living, Miss Morland; and the property in the place being chiefly my own, you may believe I take care that it shall not be a bad one.
While the General does not use terribly descriptive adjectives (see "good" and "excellent"), he does list the relative locations of many rooms and features. The narrator provides an even more detailed description in the same chapter:
The number of acres contained in this garden was such as Catherine could not listen to without dismay, being more than double the extent of all Mr. Allen’s, as well as her father’s, including church-yard and orchard. The walls seemed countless in number, endless in length; a village of hot-houses seemed to arise among them [...].
Visual imagery, combined with a bit of hyperbole ("countless", "endless") reinforces the General's description. Catherine tends to overreact to new experiences, but she is rightly awed by the abbey's grandeur in comparison to anything she has seen before.
