Sasha did notice the smile on Dan's face as he saw her discussing the wedding dress. It's only then she realized how much she has spooked her brother with her attitude.
She was a veritable airhead, and Dan must have been spooked out by the cruelty she displayed these days.
She had no choice.
Over the past ten years, Sasha has learned only one lesson. Every act of goodness would come back to bite you, if you did it without knowing the consequences.
However, this time, looking at the light in Alicia's eyes, Sasha has finally felt the satisfaction of accomplishment.
She has finally done some good.
Not alleviation, reconciliation and subjugation like she has done in the kingdom of mountains, where she prevented war by strong-arming the rebels, but the genuine satisfaction of having done a good deed that made someone happy from the bottom of their hearts.
Dan proposed a new deal upon reaching the Thors.