My cousin with dementia had a vicious cat, it would scratch and bite her, but she thought it was a good cat. It had cancer, and she spent $$$ on vets and treatment. When she went into memory care, the cat was taken to vet. She kept asking about it, finally we told her that cat was adopted by nice family with 2 children who loved the cat. She stopped asking. She thinks she is in Florida in the Bronx NY, and she is safe and being cared for now. Not easy when someone has dementia. Logic doesn't always work, you have to figure out the best/safe way to handle the situation, you need to be the "parent" now. All the best wishes to you during a difficult time.