https://journal.chestnet.org/article/S0012-3692(16)32653-8/fulltext
Tell your wife to stop eating all sugars. I had a remission of all symptoms with a diet of only steamed fish, rice and vegetables for 6 months. Drink only fresh water. No sugary drinks.
I also had PN and went almost zero carb and had immediate relief. Even now after 2 yrs when I eat some carbs like bread and pasta I start to have numbness. There is an excellent book called Sugar Crush by Dr Jacoby “What Grain Brain did for wheat, this book by a leading peripheral nerve surgeon now does for sugar, revealing how it causes crippling nerve damage throughout the body—in our feet, organs, and brain—why sugar and carbohydrates are harmful to the body’s nerves, and how eliminating them can mitigate and even reverse the damage.”