Different meeting AU

In this timeline, Jane Bennet catches the eye of Darcy's uncle's eldest son (Colonel Fitzwilliam's older brother), the (future?) Earl of ---. His family (including, of course, Lady Catherine) is very unhappy with the match, and Mr Darcy goes to try to talk some sense into his cousin – only to meet the unsuitable girl's younger sister, Miss Elizabeth Bennet.

How would Lizzy react to a Mr Darcy who's explicitly out to ruin Jane's happiness? (Or maybe Jane isn't in love with Darcy's cousin after all, but knows that marrying him would save her family? How would that affect the Lizzy/Darcy dynamic?)