AVC is apple cider vinegar. You can either get filtered from a health food store, or the stuff off the grocery store shelf. It will work fine. It will help with the brain swelling.
Good that she will eat and drink if you hold her still. Does she constantly thrash around when you put her down...
Hi there and welcome to BYC!
I always hate to see birds suffer like this. I doubt this is Mareks disease, as this causes paralysis in poultry, but it comes on slowly. I would start by giving her an overall exam to rule out ANYthing that might cause this thrashing.
I am guessing she hit her...