Prior to Pemberley, she respects and esteems Darcy, but wants nothing to do with him.

At Pemberley, she truly realizes what a wonderful person he is. Added to that, his changed behaviour complements the favourable impression given by the housekeeper. While leaving Lambton, she realizes that she is at last open to the thought of marrying Darcy.

But, I suppose absence does make the heart grow fonder. It is back at Longbourn, that she has completed the journey, and is finally in love with Darcy, though still not sure of him. No wonder she does not confess her feelings to Jane- they go through a lot of transformations, and maturation processes.