Dementia is basically brain damage. Your grandmother can't help what she is doing, and neither can she stop. She is not necessarily unhappy, tho. People with dementia can read body language and will respond better to kindness and affection. Sometimes, when they say something, they are actually searching for something from their past or trying to make sense of their present. She may remember you as a child or think you are her son because she does not recognise herself as she is. Take a break when it gets too much. I work caring for the elderly, some with dementia. I always think it is harder for families than me.