With Frozen 2 digging into her origins and putting her through a transformation, Elsa is now immortal, taking her place as more of a spirit than a person. While the original Frozen left Elsa’s origin as simply “she was born with magical ice powers”, the sequel dove much deeper into the mythology and history of not only the character, but the Kingdom of Arendelle and beyond.
From their early days, Anna and Elsa knew about the four spirits, the usual elements of earth, fire, water, and air. Through Frozen 2’s adventure into Northuldra, however, they find that there’s a fifth spirit to unite (and command) the other four. Their mother and father, by uniting Northuldra and Arendelle, respectively, were gifted Elsa, a daughter with magical abilities. Not only that, but the movie reveals Elsa is the fifth spirit herself.
This makes her far more than just another person, and her transformation in Frozen 2 suggests that what makes her different isn’t just symbolic, but that she’s actually an immortal spirit - after all, earth, fire, water, and air could all be considered 'immortal', so it makes sense that the fifth spirit, i.e. Elsa, is too. Elsa’s transformation happens in Ahtohallan, where she’s overcome literally and metaphorically by discovering the secrets of the past. While discovering the truth about Arendelle’s history with Northuldra during the song “Show Yourself” Elsa changes her appearance before being frozen over completely. Elsa is famously not bothered by the cold, but this is something different. It’s clear just how much so by Olaf: Elsa’s magic has kept Olaf alive so far, but now he fades away. This leaves Anna to solve things by destroying the Northuldra dam all on her own.
When the dam is destroyed, Elsa thaws out and has clearly been changed in some way. While she’s always been powerful, she’s able to stop the flood threatening to take out Arendelle without much difficulty. She barely gets there in time with the help of the water spirit, but using her ice to stop the water seems almost easy for her. When she next sees her sister, Anna immediately points out how different Elsa is now.
While Frozen 2 doesn’t spell it out, the symbolism is clear. Elsa died and was reborn in Ahtohallan, coming back more powerful than she was before. The reveal that she’s the fifth spirit doesn’t just mean she’s a more powerful magic user than before. She died and was reborn to take on her true form like has happened in so many stories before. With that transformation, Frozen 2 has made Elsa an immortal spirit now. Like how Frozen 2's other four spirits appear as animals but more than just that, Elsa still appears human but is more than just that. Elsa hasn’t lost her humanity, but she’s so much more than just a person.