I say either blindness, something that would make her mute, or a loss of some limb. It hard to decide, though I'm kin of leaning toward making her mute somehow(as blindness would make it really hard for her to interact and take care of dragons, as well as ride Aurora). :/ Don't know how I'd make her mute though. I guess if couldn't think of a way to make her mute I could make her loose a hand(or even arm) but if I did that I would want her to have some sort of mechanism like Hiccups, but that isn't likely considering to have a working hand would be almost impossible for the vikings to build I would think XD If they did it would probably look something like
this just with the thumb missing as well. Maybe the wristband piece would somehow react to pressure from the muscles in her wrist and that pressure would make the hand open and close? Just a thought anyway.
Which do you think would be better? Blindness, mute, or missing a hand?