Queen Iduna of Arendelle,Norway suffered a case of severe hypothermia during her first pregnancy. For that reason, she was rushed to a hospital where she fell into a coma for several weeks. After those several weeks, her sickness passed on to her first daughter Elsa right when she was born. Thus, Elsa officially had ice powers. Queen Iduna decided to keep this incident a secret simply because she just didn't want anybody to know how Elsa got her ice powers otherwise Queen Iduna would've gotten herself kicked out of the throne for good. She didn't even want to tell Elsa how she got the ice powers. That is why Queen Iduna and her husband King Agnarr decided to move out of Arendelle just so that no one would be able to ask them about Elsa's ice powers.