I would agree with Total Equine if you find you need to change her feed. Just do so slowly as I’m sure you’re already aware. Our Arabian mare had the same issue when we put her in a boarding location. Is it possible for her to be put in pasture versus a stall? It is natural for them and they tend to have less anxiety when they are not walled off from the outside or the herd.
"Your frustration begins where your knowledge ends. "