In the first movie it's strongly suggested that Elsa's parents were completely baffled by her powers and hence they weren't able to help her much in learning to live with them. From the second movie we learn that this can't have been the case:
where Iduna comes from, such talents are not unknown (although presumably rare). The Northuldra leader finds it unbelievable an Arendelian could have magical abilities, because in their society these things are associated with a certain relationship with the forces of nature and have a purpose within that context. As a Northuldran, Iduna would have understood all of this. If nothing else, she could have told Elsa that she wasn't alone in the world and that she has her powers for a reason which will become clear later on. This could have been of great comfort.
Yet she kept this to herself.
In one of the first scenes from the second movie their father tells the girls about the incident in the Enchanted Forest
and how "somebody" saved him. Anna says she loves whoever that person is, and Iduna looks hurt for a moment.
This shows the screenwriters were intentionally presenting Iduna as someone who kept many things secret and regretted having to do so. We're given a plausible reason for Elsa and her family to keep her powers secret from outsiders. But are there any sources, canon or otherwise, which explain why Iduna kept so many secrets of her own?