If she likes that, save some $ and just buy USP Glycerin and add it to water, because that's all it is. ( I did this before I found Biotene, which in my experience of using it everyday is way better) Add a couple drop of mint flavor if that is important to her and you have spent pennies for the same thing. The label says it has some enzymes in it, but laboratory testing (by Laclede who have a patent on adding enzymes to oral care products) shows the levels to be so low as to be inconsequential to oral health. The enzymes are what are so expensive in the Biotene products. But for each person it is what relieves the dryness.

David is right, the oral environment is constantly changing and what works today (or not) will be different in a month or two. Keep trying to find things that work. Experimentation in this and in what you can eat and drink yields a workable life down the road.