There's something to be said about no secrets. There's very little else they can fuck up in their- what, relationship? Acquaintanceship? They don't address it. No use dwelling.
Anna still has the weight of cheating on her, but it's lessened. Elsa didn't forgive her that night, but Anna's starting to wonder if Elsa even thinks she needs to be forgiven. Because Elsa isn't happy. Maybe... maybe she wants Anna's forgiveness. Or God's. Someones. She wants someone to tell her she didn't make a mistake, and Anna... isn't that person.