Austen is using satire here to ridicule the upper class, that being Lady CdB
'Her air was not conciliating...she said was spoken in so authoritative a tone, as marked her self-importance.'
“Miss De Bourgh is far superior to the handsomest of her sex, because there is that in her features which marks the young woman of distinguishes birth.’
The speaker is saying that Miss de Bourgh's high social status and noble family make her seem special and better than others, even if she isn't the most physically beautiful. It reflects a time in the Regency Era when being from an important or wealthy family mattered more than looks or personality.
