According to USA Magazine —
Here’s what Producer Peter Del Vecho originally had in mind:
“So when we started off, Anna and Elsa were not sisters. They weren’t even royal,” he told the magazine. “So Anna was not a princess. Elsa was a self-proclaimed Snow Queen, but she was a villain and pure evil — much more like the Hans Christian Andersen tale [The Snow Queen].”
According to Del Vecho, Elsa became wicked because she was previously stood up at the altar on her wedding day. She decided to freeze her own heart to safeguard herself against the pain of future heartbreak. This would have led viewers to believe that she was the frozen-hearted individual bound to destroy Arendelle, as stated in a prophecy.
Amid Elsa’s snow monster war, undercover antagonist Prince Hans launches an avalanche on Arendelle, forcing Anna to convince Elsa to stop it with her ice powers. So it turns out Hans is the bad guy from the prophecy and Elsa’s heart finally thaws because of her selfless act…