How old is she? Can you post some pictures? How many birds in how much space?
First thing I would do is give her a super B complex tablet or capsule, any brand, from any drugstore. Riboflavin deficiency can cause curled toe paralysis if deficient, which is not uncommon, and thiamine deficiency can cause all kinds of neuromuscular symptoms. Give once a day to see if it helps, it can take some time, but there is no risk of over dosing those, the B's are excreted when there is extra. Get a look at her droppings, make sure her crop is functioning properly, see if it feels empty, full, hard, soft and squishy etc. and then check first thing in the morning before she's had food or water, it should be empty then. Also check her keel bone, see if it's very prominent, or if it's well muscled. If she's laying age, do you know when she last laid?
I would crate her in a wire crate for now, so you can monitor eating, drinking, droppings, etc. You can put rolled up towels around her to help keep her upright, or you can use a sling for periods to keep her upright and make it easier for her to eat, drink and poop. Examples below, you do need to supervise in those so she doesn't hurt herself trying to get out.
With sudden onset it can sometimes be egg binding, so check for that if she's laying regularly, or possibly a toxin as well. Look around for anything she could have gotten into, fluids leaking from machinery, moldy feed, something rotten, etc.