Elsa doesn't have an answer. There's nothing she can really say, not while Anna is so distressed.
So she sits on the end of the bed and bites her lip. Anna isn't looking at her. She's clutching her stomach with her eyes squeezed shut, and Elsa wants to hug her just as Anna did in the changing room.
But she can't make herself move, so she remains where she is and answers Anna with a question of her own.
"Why did you do it?"
She doesn't blame her. Never has.
Anna didn't know.