You'll never change her. You have to arm him. But please don't expect perfect sugars. It will never happen, and it will drive you crazy. Learn to deal with her meals the best you can; there will be many other challenging events.
I've been living with my mother's occaisionnal cooking my whole life. She really cares, and she's tried to change many times, but she just has to lay out a feast whenever company comes. Must be a generational thing. I've learned to say "no thank you." Usually I say it three times a visit.
He also has to have sharp carb counting skills - mashed potatos, squash with brown sugar, homemade bread, gravy with flour - mothers are insidious.
I recommend you help arm him the best you can, trust him, learn from each experience, and enjoy her company and attention while you still can.
