I'm so sorry Pixie is still struggling. Have you tried Melatonin yet? It is used for thunder fear and July 4th fear, and some have very positive results. It is easily obtained via Target, Walmart, the grocery etcetera. You'd give 3mg if you think a storm is coming; don't get the extended-release kind. You can try cutting it in 1/2, but they see more efficacy in 3mg, even in small dogs. Wylie takes Melatonin 3mg every day for his Cushings, no side effects.
Thunderstorm Anxiety - VetInfo
I'm sure this has been asked, but...knees?