They had said they would only be gone for two weeks. They had business to attend to in a kingdom across the water, but it was supposed to be a short trip. Her father had given her his word that it would. Anna had hugged the both of them goodbye, and Elsa had stood back, wishing they didn't have to leave at all.
Promises like that weren't always a person's to give. Not when dealing with the sea.
And Elsa couldn't even attend the funeral.
She'd been holed up in her room for days now, not letting anybody through the door. How could she? Her entire room had frozen over, snowflakes hanging suspended in the air. And, more important than that, her sister, Anna...
Well... It was just better that Anna not come in. Ever. And now that their parents were gone, Anna had been to her door again and again, trying to get her to at least speak.
"Elsa, please... I know you're in there. People are asking where you've been. They say, 'have courage,' and I'm trying to. I'm right out here for you." Elsa didn't speak, sitting on the floor with her back against her bedroom door, listening to her sister desperately try to get an answer out of her. "Just let me in? We only have each other, it's just you and me. What are we gonna do?"
Elsa didn't know what to do. With their parents gone, she really was alone. Anna was there, offering to be there for her. But Anna's offer was the one that she absolutely couldn't accept. Elsa knew that the only thing she could do was leave when Anna asked her one simple question, "Do you want to build a snowman?" Because the answer she wanted to give, wanted desperately to speak through the door, was, "Yes, I do."
[OOC: NFB and NFI, naturally! Grabbed right from near the start of Frozen.]