I've seen her in a chair plenty of times, but never in a wheelchair, not even on danboru. Doesn't mean pics like that don't exist, but the rarity makes it feel like fanon.
I always interpreted her sitting down as a way to make her look more regal and aristocratic. British women in pop culture sit down and have tea constantly, that's how you know they're British.
I still hope it's like Apocrypha that starts with the end... Since they said that the battle would be like an RPG and the protagonist finished the chapter full of holes, maybe he revives as fem hakuno... Pls pls pls die and revive as fem hakuno :(