4.3.1: Olivia brings a priest to her garden and proposes to Sebastian (who she still believes is "Cesario." They run off to get hitched.
5.1.1: Olivia yells at "Cesario" for being a neglectful husband so soon after their marriage vows.
5.1.7: Olivia thinks her husband is in love with Duke Orsino when "Cesario" chases after the Duke.
5.1.16: Olivia is psyched when Sebastian shows up and she realizes that she has married Viola's twin brother and not "Cesario."
5.1.27: Olivia learns that Maria and Toby have been playing a joke on Malvolio. She explains to Malvolio that she never wrote him a love letter. When Malvolio runs off and swears revenge, Olivia is the only one to express regret for what has happened to her steward. Still, she parties with the others because she's newly married and Viola is engaged.