The king and queen rushed the girls to the trolls, mysterious healers who knew about magic. A wise troll named Grand Pabbie saved Anna by removing her memories of Elsa's magic. He explained that she was lucky to have been hit in the head, not in the heart.
The troll told the king and queen that Elsa's powers would only grow stronger. "Fear will be her enemy," he warned.
The King and queen knew they had to protect their daughter. ....
FROZEN Storybook Collection
This is from the Children's book FROZEN. I'm not sure what "Elsa's powers would only grow stronger" is trying to convey in this context. Also, in "Fear will be her enemy,", is 'her' referring to Anna or Elsa?