Producer Peter Del Vecho :
"Frozen went through many different iterations, but here are some common elements from some of the early drafts: Frozen was to open with a prophecy that “a ruler with a frozen heart will bring destruction to the kingdom of Arendelle.”
We’re then introduced to Anna, our pure-hearted heroine, and Elsa, an unrelated evil Snow Queen. We learn Elsa is a scorned woman; she was stood up at the altar on her wedding day and froze her own heart so she would never love again. Both Elsa and the audience assume she’s the villain from the prophecy.
Fast-forward to the final act: Elsa creates an army of snow monsters to attack our heroes while Kristoff has “a Han Solo moment” and comes to help Anna. To halt Elsa’s attacking army, the two-faced Prince Hans triggers a massive avalanche — not caring that the avalanche also puts Anna, Elsa and all of Arendelle in jeopardy. Anna realizes Elsa is their only hope, so she convinces her to use her powers to save the kingdom.
The twist is that the prophecy from the beginning is actually not about Elsa, but about Hans — he’s the one with a metaphorical frozen heart because he’s an unfeeling sociopath. Elsa’s heart is then unfrozen allowing her to love again."
Why the ending was changed
“The problem was that we felt like we had seen it before. It wasn’t satisfying. We had no emotional connection to Elsa — we didn’t care about her because she had spent the whole movie being the villain. We weren’t drawn in. The characters weren’t relatable.”
“Making them related led us to the idea of her living in fear of her powers... Now we had a character in Anna who was all about love and Elsa who was all about fear. That led to making Elsa a much more dimensional sympathetic character, and instead of the traditional good vs. evil theme we had one that we felt was more relatable: Love vs. fear, and the premise of the movie became that love is stronger than fear.”