Hi there
As a vet, I just have to ask how much poultry medicine your vet does, as I am a mixed practicioner, and I don't see chickens very often, but do see a lot of dogs and cats off balance from ear problems.
However, I have seen chickens do something very similar in terms of balance when they have Marek's disease, which is a type of tumour of the nerves. They can be very unbalanced and unwilling/unable to get up and move normally, though may be able to sit happily.
I am very much the same as you with my animals and try to give a bit of TLC to nurse them through things rather than assuming the worst, but if it was Marek's disease, there is nothing that can be done.
I think if she's improving, then keep at it, and she could well come right, so

for you both
Suzanne