Though Iduna had once lived with the magical spirits in the Enchanted Forest, she and the rest of the Northuldra didn't have control or possession over them. It was therefore unusual for Iduna to witness another human actually possessing magical powers.

Is Iduna magical?

Iduna didn't have magical powers in the same way that Elsa does, but like the other Northuldra people she had the ability to perform magic by interacting with the spirits of the forest.

Did Elsa's mother in Frozen have magic powers?

Elsa's Mother Already Comes From A Magical Background

While the original Frozen implies that Elsa is the only magical member of her family, she discovers that her mother was one of the Northuldra in Frozen 2, and likely interacted with magic regularly.