Is she able to see to eat and drink?
Crested birds sometimes need feathers trimmed away from their eyes.
Does she always stay bent over like that?
I'd be inclined to give her 400UI Vitamin E daily along with some egg or tuna, this is in addition to her eating her normal feed.
Check to make...
Please post photos of the birds?
How are they housed? Photos?
What do you feed, including treats?
Are any laying eggs?
Corid does not cause deficiency if give at the correct dose and for the correct time period. Did you give vitamins when you gave Corid?
I'd stop all the vitamins, you've...