Disney has yet to reveal the plot of Frozen 3, but it will likely see Elsa continuing to embrace her powers, and that means the sequel must preserve a design tradition established in the previous films. Frozen and Frozen 2 follow sisters Anna and Elsa, the latter of whom possesses the extraordinary ability to control ice. When the Disney series opens, Elsa has spent her whole life suppressing her magic, the result of an unfortunate childhood accident. Throughout Frozen, she learns to accept her powers and use them for good. She repairs her relationship with her sister and becomes queen of their home, Arendelle.
https://screenrant.com/frozen-3-elsa-hair-journey-symbolism/