It's always interesting when people compare Elizabeth to Lydia, and they do have a few similarities, but I personally viewed a pre-Darcy Elizabeth as well on the way to becoming her father: intelligent, witty, insightful and independent yet always mocking rather than genuinely connecting, bantering rather than having real and serious conversations, retreating and detaching rather than engaging.
And that's why even though the focus is usually on how meeting Elizabeth transformed Darcy for the better, I see Darcy as just as integral to Elizabeth evolving into a far better person. Darcy is serious, complex, mature, responsible, and painfully honest - he compels Elizabeth to take life more seriously, to rethink her judgments, viewpoints and perspectives rather than just remaining complacent, and to engage in deeper discussions and more candid self-introspection than she would have otherwise!
