One of the more interesting things about Elizabeth that is sometime overlooked (especially in film versions) is that she is an upper class gentleman's daughter. She is a lady. She is not a country bumpkin with no grace, manners, civility, education or talent (as her younger sisters are--Mrs. Bennet must have gotten worn out as well as depressed after raising the first two daughters and finding yet another daughter rather than a son to break the entail). She can very easily be conceived of as of the same kind of young woman as Jane Austen herself, and no one accuses Jane Austen of being countrified though a clergyman's daughter and though not living in London.
The qualities that go with her description as a lady are her ability to reason. Remember, her mental acuity is so keen as to be able to keep up with Darcy himself when they exchange barbs at Netherfield during Jane's illness and later during the ball. Similarly, she is keen enough to thoroughly denounce Darcy with irrefutable logic, though she got some of her facts related to Wickham wrong, when he proposed in Kent and she proved he was not acting like a gentleman. Another quality that goes with being a lady is that she can stand up to even the likes of Lady de Bourgh who believes that she can utterly cow Elizabeth with her superior rank and power. Yet, since Elizabeth knows she is a gentleman's daughter (even though he wasted his wealth while vainly expecting a son) and a lady, she can reject Lady de Bourgh's demands and intimidation and send Lady de Bourgh completely unsatisfied with the results of her visit to Longbourn.
"In marrying your nephew, I should not consider myself as quitting that sphere. He is a gentleman; I am a gentleman's daughter; so far we are equal. ... Whatever my connections may be," said Elizabeth, "if your nephew does not object to them, they can be nothing to you. ... You can now have nothing further to say," [Elizabeth] resentfully answered. "You have insulted me in every possible method. I must beg to return to the house."