What events in the plot cause Elizabeth to reflect on Darcy's character and their future relationship?

Mrs. Reynolds describes Darcy in his youth as a sweet child, a surprising definition for Elizabeth.

Darcy arrives and behaves in a very polite fashion around Elizabeth which embarrasses her because she has behaved badly.

His attention and love to his incredibly shy sister help Elizabeth see him in a more positive light.

Elizabeth and Darcy share mutual guilt in not having told everyone about Wickham and his bad debts.