I have tried many stevia brands, I had one that I really like then they went and changed it so it is like all the others for me now.
I have tried the Monkfuit sweetener in my tea and it has worked well but it doesn't seem to be inexpensive. I have also used Xylitol in some sauces and for some baking with good results. I have read that it may cause a laxative effect if to much is consumed, but I have never had this issue. I use it in my pumpkin custard. (Pie Filling)
I still like the good old pink packets of saccharin the best for my tea. I don't recall if I have ever tried to make any type of sauce with it, maybe I will try that.
I am diabetic also, not bad, but still classified as being. I make a BBQ sauce that we like the recipe wants 1/2C brown sugar. I don't know exactly how much it makes but it starts with almost a quart of wet ingredients. Using the Heinz no sugar added ketchup I get roughly 112 grams of sugar to a batch which say I reduce by 30% I get 22oz so I end up with about 5 grams sugar per oz. If I sub the brown sugar for 1/2c xylitol and 1T Molasses I end up with roughly 41 grams per batch at 22oz that is under 2 grams per ounce.
I never measure how much I use but I figure for a rack of ribs 3 to 5 oz, and if you mix he sauce in with your pork you will use less than if added directly on the sammie.
Good luck on getting something made that resembles your normal sauce it can be done, and it is great you are looking out for your SIL.