Accident at Elsa's ice palace

When Anna went to visit Elsa at her ice palace, an accident occurred in which Elsa again unwittingly struck Anna, this time in her heart, with her powers.

Prelude
After her icy magic was exposed during the night of her coronation, Elsa fled Arendelle to the North Mountain where she built her ice palace. Anna, asserting that her sister never meant to harm or threaten anybody, volunteered to go after Elsa herself and rode off on her horse. She later arrived at the ice palace to talk with Elsa and convince her to return.

Accident
Anna told Kristoff and Olaf to wait while she went to talk to Elsa. Upon entering the ice palace, Anna was awestruck by the intricate design and grandeur of its interior. She called for Elsa, who was delighted to see her but chose to keep some distance from her. Anna apologized to her sister for what happened at the coronation, to which Elsa harbored no ill will regarding the incident, but suggested that Anna leave the palace.

A minute later, Olaf entered and introduced himself to Elsa. Elsa was surprised to see that the snowman she had built was alive. However, when Anna said they could once again be as close as they were when they were children, Elsa had a flashback of the previous accident, prompting Elsa to flee upstairs, fearing for Anna's safety. Anna gave chase to reason with Elsa, but Elsa insisted that Anna leave the palace and go back to Arendelle, where she would be safe from her sister's powers.



When Anna told Elsa that she had triggered an eternal winter on the kingdom, Elsa was shocked and began to panic; a blizzard began to swirl around her, growing stronger as her fear intensified. As it reached its peak, Elsa lost control of her powers, causing them to burst out in all directions; this struck Anna in the heart.

Elsa was shocked when she saw Anna doubled over on the floor. Just then, Kristoff, having heard the commotion, rushed to Anna's side with Olaf, but Anna wouldn't give up on Elsa, promising they could figure out a solution together. Not seeing reason, Elsa conjured Marshmallow to throw them out of the palace. Anna, Kristoff, and Olaf managed to lose Marshmallow by falling off a cliff, though not before Marshmallow warned them not to come back.

Aftermath
Once again in solitude, Elsa desperately made attempts to control her powers by suppressing her emotions as her mind raced. Once again, she became overwhelmed, and her guilt and fear caused ice shards to fill her palace.

Meanwhile, Kristoff noticed that Anna's hair was turning white. Deducing that it was from Elsa striking her, he took her to the Valley of the Living Rock. Kristoff brought Anna to Grand Pabbie, who informed her that there was ice in her heart and that only an act of true love could thaw it. Supposing that a kiss from Hans was what Anna needed, Kristoff set off to take Anna back to Arendelle.