Hello @ally3. After reading your question, I had to search my memory banks for the products I used after being treated with radiation for cancer of the Pyriform Sinus, which is near the vocal cords. There a quite a few products that proclaim to relieve dry mouth. One great produce is XyliMelts.
The following is the online definition of this product from AI: "These oral-adhering discs stick to your teeth or gums to relieve persistent dry mouth. They are made of saliva substitutes that mimic the properties and functions of natural saliva, such as lubricating, moisturizing, and protecting the mouth. XyliMelts can be used during the day or while sleeping and may help with symptoms such as frequent thirst, sticky dryness, or discomfort in the mouth or throat. XyliMelts are also sugar-free and contain xylitol, a natural sweetener that may prevent tooth decay and plaque."
I kept water around constantly the first few years after radiation. Please tell your family member that time usually helps a great deal. She may even forget the products she used to help relieve the dryness! It may take a few years, & hopefully she will return to some form of normalcy. Best Wishes.