"You're wearing mother's scarf. You do that when something's wrong".
I've been thinking about Elsa and Iduna's scarf and would like your views. Logically speaking, Elsa probably did not wear the scarf during Frozen 1 because A) it's never seen (granted that the scarf plot device is a new F2 introduction) B) Anna has not seen Elsa for years and would not have seen her troubled and wearing the scarf till after the events of F1 C) Elsa was still in her conceal don't feel phase.
So if that is the case, then it begs 2 questions. 1. When did Elsa rediscover the scarf and why? And 2. Actually, what is the history of the scarf? I'll air my thoughts about #2 first.
We know that the scarf is Northuldran, meaning young Iduna had it since before the Arendelle-Northuldra War. In fact it may be a family heirloom. So Iduna must have had it with her when Gale helped her rescue Agnarr and helped them both escape in the cart. I had hoped that the cloth Gale covered Iduna with was the scarf, but it isn't.
Nevertheless, Iduna brought it with her and she held on to it through her years in the orphanage, and all the way till she met Agnarr, became Queen and moved into the castle. Altho we don't see it in F1, in my own head I retcon that the scarf has been there all this while and they would have wrapped Anna in it while seeing the trolls. (retcon)
As @hafanforever has said, Iduna was wearing the scarf when she told Agnarr the truth about who she is.
Obviously the scarf didn't go onto the doomed voyage or it would have been lost. So where did Iduna keep it? I'll come to that later.
So to answer #1 (and this is just my thoughts) could it, could the answer be during OFA? It's Arendelle's first Christmas in forever so it's December of the same year that F1 took place (which was in July) so, fairly soon after F1. Elsa recalls past celebrations with the Yule bell, which brings back happy memories of her parents, washing away the years of unhappy memories.
But immediately she's charged by guilt.
"it's my fault we don't have a Christmas tradition"
But later on, she goes into the attic after hearing Anna messing around. And Anna finds her viking helmet, sorcerer's cloak and of course, dragon feet! (om nom nom)
They next open Elsa's old chest and find gloves and Sir jorgenbjorgen and of course all the Olaf traditions Anna made.
Now could it be that Elsa then went on to open a chest of Iduna's things and found the scarf??