No, this is legitimate crit, especially if it makes it difficult for you (and maybe others) to play with me! Thank you for bringing it up with me, anon.
While it's true that I see Elsa's mental well-being as very dependent on Anna, and Anna's absence in the game being a con, there are also pros to being in Kiseki that don't exist back in canon - here Elsa has more of a support net; people are familiar with, and not afraid of, magic; and she can't isolate herself to the same extend she does back home. These are all things I see helping with her development, and even if ultimately she might not be truly well without a canon update and/or Anna's presence, I'd like to explore that alternative way of gaining confidence/control, if that makes sense. I do plan on canon updating her eventually, but I want to work on establishing Kiseki as more of a safe place for her to be herself in before doing so, if that makes sense? Otherwise, unless I bring her from after the movie ends she'll just be worse about the isolation. De-aging her is something of a first step towards this, or at least that's my plan: it's a chance to deepening/establishing some CR, being more open about her powers, and confirming to other characters/reminding herself that she used to be able to control her magic despite what adult!her believes.
I admit I don't have a super detailed plan for how to go about all of this, but I hope this reply is useful to some degree? Whoever you are, anon, I guarantee that I do want to continue my CR with you, and I definitely don't want to make it a struggle for you.