So what exactly are you testing for? Are you waiting on an ABV test?
Have they done a CBC and Chem Panel? To you, does it seem neurological in nature? Has she always been this way, has it become worse?
What did the xray show? What is her weight and how much formula are you feeding? Did she have any infections present?
I know VERY well what you are going through. My vet wanted nothing more than to put down my BG at almost that same age. She swore he had PDD and did so little to explain anything to me. PDD is nearly impossible to diagnose in a live bird and it becomes the catch all when the vets don't know what's wrong. If the vet feels so strongly did she put your baby on celebrex?
That's my next question, when vets don't opt to treat, they are usually going to recommend ending life. Then you get the necrospy back that showed no evidence of PDD.
You can not clearly suspect PDD until you exhaust all other options to the cause. Had I listened to my vet, my BG would not be here today. My BG had avian gastric yeast NOT PDD as thought.
Take a breath, slow down. Have your vet write a prescription for celebrex while you wait. Don't do anything without talking to us. Even highly respected Avian Vets are wrong sometimes.
What's the history of this bird? Where did you get her and have you contacted them?
EDIT Are you still using the dexamethasone? Why was it given? I would discontinue use of that one.