Previously on 12 Months of Frozen:
I'm not going to lie: this idea came out on the spur of the moment, as part of an instinctive reaction of "You want Anna to be the main character? Fine, I'll GIVE you Anna as the main character, and it'll STILL have more Anna&Elsa interaction. Because I can."
Just so you know where this is coming from.
As mentioned previously: Anna and Elsa are still ladies of color. Just in case you forgot. Also, for the sake of having some variety between the Disney princesses, I'm going to go ahead and say that they're both short and have waists larger than an inch.
(Also you should go check out this redesign of them as Inuit, because it's really cute.)
Because this is now officially Anna's Movie, we don't see Elsa at the beginning — instead it's like the beginning of, say, How To Train Your Dragon, where we frontload some of the important info right off the bat in a voiceover or song. Key points: Anna's parents died a few years ago, her sister was lost, and their land was cursed with perpetual ice and snow, which understandably has been not so great for things like inter-kingdom trade. Not that we're really going to get into how the import/export business suffers when your major travel routes are prone to avalanches, but we get the idea that Arendelle, which used to be a thriving hub of people, has suddenly been thrust into a forced, and painful, isolation.
The song/voiceover is Anna's way of making all this into a sort of story, something she could be telling to one of the paintings — a form of abstraction to help her think about it without breaking down. Not a fairytale, because she's ambivalent about fairytales, but a history, because she loves history.