I have a small dog that had a bone disease and had to have the head of her femur (leg bone) removed. I have always been very careful about her weight. My mother has moved in with me and I have asked her to not feed my dog, have TOLD her not to feed my dog, have explained the situation, etc--NOTHING works! She always fed her dog from her plate or her hand if she had a snack. I don't want that for my dog. She says that once you get to be in your 90's your allowed to do what you want. I don't know if that is "her" speaking or her "dementia" speaking. I lost my mate recently and I don't want to lose my precious dog too soon as well. I don't want to have to tell my mom that she'll have to go to assisted living but I am a my wits' end! HELP!!
Also your mom does have the right to do what she wants at her age - with her own pets, if she had any. The "rule" about being allowed to do whatever you want at that age applies only to YOURSELF. You are not "allowed" to cause harm to others. I have the right to eat my way to a heart attack, but I don't have the right to force feed someone else into one. I have the right to smash my own furniture to bits, but not someone else's furniture. I would try repeatedly reminding her that it's not her dog, it's yours, and that you set the rules for your dog.
But if that doesn't work, the kennel idea really does seem like a good one.
Preventing the undesired behavior, in this case feeding the dog, is better all the way around. Keep Dog away from Mother when Mother has food.
Condolences on your recent loss, and on your beloved pet's health issues.
Having Mom move in with you is a huge change in your routine. I think it will go more smoothly if you learn all you can about her condition, dementia. Nobody is born knowing how to cope with that huge challenge. I remember all the explaining I tried to do with my loved one in the beginning. I could have saved a lot of frustration for both of us if I had simply understood that that approach was no longer going to work.
Come here often. Hearing other people's experience can help you get up to speed faster.
I'd read a lot about what to expect down the road as she progresses, so, you'll have an idea what may come. It really is surprising. I hope you can find some help for your situation.