Just because it's a mostly respectful debate with someone I respect, I'll keep going.
1. With what you stip to there, that Elsa automatically defends herself against an incoming attack by freezing it, shows that, even if she's not consciously doing it, her POWERS include some kind of autodefense that work at significantly-faster-than-normal-human speeds. And again, for this particular situation, it makes trying to punch her in the schnozz a really bad idea.
2. I would also posit that Elsa realizes that she's in trouble, but she is so inexperienced with her abilities that she has no idea that she can do what she did there. She's also never been shot at in her life. So yeah, she has a normal human flinch reaction away from the bolt. But she clearly also manifests her powers to defend herself, and again, does it basically instinctively, and faster then the already-fired bolt can cross the distance.
3. I'd like you to clarify your argument against her repeating what we actually see on screen. If you are arguing that she's presented specifically and explicitly as someone with normal reactions, I'd like for you to point out where. If you're arguing that she can't be somewhat quicker than normal with her powers because it's only shown once, well, I'd ask to see the times where she either FAILS to act quickly with her powers, or she's explicitly shown not to be quick with powers. Because it seems like you are either arguing that the feat is an outlier, but an outlier needs to have contrary evidence and there isn't any of that, or that it's, I dunno, an unrepeatable accident, and again, that's not really shown by the material.
Basically, I don't think the things exist to show that she can't consistently do what she does the only time she has to: she really only has the one speed/combat feat. And I agree that it's not amazing or super ultra dominant and conclusive, but it's all we have.