Rumor has it that Lady Bracknell was a combination of Wilde's own mother, Lady Wilde, and Lord Alfred's own mother, Lady Queensberry. Seems like his mother takes the cake on the dead-on character for this.
Lady Bracknell is a woman of extreme mannerisms, she is a major-league snob with little disregard for human emotions as for example when he says that "losing one parent may be seen as a tragedy, but losing both parents seems like an act of carelessness"
She is entirely devoted to social ranking (her questions about Cecily's state of financial affairs prior to letting her marry Algy) and her equal questionnaire of Jack/John/Earnest when he was contemplating marrying Gwendolyn.
She is so elitist that Jack Worthing finds himself having to add that he was left in the terminus, but "in the Brighton line", meaning that even the route of the terminus would make a difference to Lady Bracknell. Also, she drops names (working together with the Duchess), and is careless about the feelings of others.
Victorian society was just as elitist, "holier than though", living above their means, hypocritical, censuring, snobbish, and name dropping as Lady Bracknell was. Her mannerisms make the entire situation so extreme that is what makes it a satire of her.