Jane Austen actually very seldom uses metaphor. Her preferred writing style is much more direct, saying exactly what she wants to say without making allusions or comparisons. I certainly cannot find any metaphors used to describe setting or plot. However, I was able to find two very weak examples of metaphors, even though they do not contribute to setting or plot.
One takes place soon after it has become known that Lucy is secretly engaged to Edward. When conversing about the matter with his sisters, John Dashwood compares his wife's reaction to the discovery as that of an angel's: "She has borne it all with the fortitude of an angel!" (Ch. 37).
A second example of a metaphor can be found earlier on in the text. Mrs. John Dashwood, Fanny, is described as a caricature of her husband: "Mrs. John Dashwood was a strong caricature of himself" (Ch. 1). This serves as a metaphor because of course a person cannot really be a caricature, which is an exaggerated, comic, or gross representation.