Old thread, but here is a worst case possibility for you: Your dog or cat could die. Really.
I have a 101-year-old mother with both dementia and narcissistic personality disorder (not caused by the dementia; she's always been narcissistic, and I had to undergo years of healing from her self-absorbed behavior in order to create a somewhat successful life for myself; plus, I'm a former psychologist, and I am fully able to diagnose narcissism). I've cared for her for 9 years, in her own home with my husband. My husand and I both lost our jobs and careers during the recession, have never recoverd financially, and lost our own home to foreclosure--moving in with mom solved two problems at once, her need for a caregiver and our need for a living space.
I had an Italian Greyhound (one of two dogs we had) when we moved in named Flash. Mom had only very, very mild dementia years ago, but has always managed to sneak people food to my dogs whenever my back is turned. She has been told hundreds of times not to do this, but her narcissistic need to control made her defiant when we talked to her about it. Also, her narcissistic need to be right caused her to claim that we were wrong, that people food doesn't hurt dogs, that she knows better than the vet because "I've had dogs for years," etc. etc.
Feeding dogs either onions or grapes can cause a lethal malady called Hemolytic Anemia, which costs thousands of dollars to treat long term and has a high death rate. My dog Flash contracted both Hemmorhagic Gastroenteritis (another sometimes fatal disease triggered by bad food) and Hemolytic Anemia after living with Mom for a few years, undoubtedly caused by the thousands of inappropriate, highly spiced people foods she snuck to him. He survived the gastroenteritis but eventually died at age 10 from the anemia, after we spent $8000 to try to save his life. We are still paying off the medical debt two years after he died. Mom never took any responsibilty for his illness, never contributed a penny for his medical care, and still denies that her defiant feeding of the dogs had anything to do with his health.
I personally took Flash's death very hard, and was depressed for about 6 months after he died. I'd never had a dog I loved as much as Flash, and knowing my Mom killed him has been very difficult to deal with. So think about whether you could deal with knowing your mother killed your dog, when it comes to considering solutions. I say lock the fridge and lock the pantry, and watch her like a hawk when she's eating, and take away any uneaten food from her immediately. It's the only way to be safe.
