Before switching food (I have never used Instinct but if it is one of those raw foods, I wouldn’t recommend) Small breeds are notorious for not doing well on raw foods. Not worth the risk for any dog (imo)
I would take her in for a veterinarian visit, senior workup complete with dental check, labs and whatever else your vet recommends (if you have not done so already).
I doubt if her symptoms have anything to do with “dry air”.
If she has had a recent vet check then I would put a call in to your vet and see what he thinks.
There are many things that could cause the symptoms you describe, it’s impossible for anyone over the internet to guess, nor should they try.
