I would try to visit mum as much as possible because she was always against going in to a care home. She showed early signs of dementia from the start although I was lucky that she always knew who I was until her passing over four years later. You talk about friends and family and what is happening in the world to keep their mind active. Nothing can prepare you for the conversations when they are in another time zone and can remember everything from 40 years ago but not what they had for breakfast. 

A few times I asked mum how old she was and she would say 54 or 72. She sometimes talked about her father who had just bought her a car and when she was even younger with her mother who died two years before I was born. She had no complaints about her final years and was always happy especially when the great grandchildren came to visit. When she was back to normal time, she still had a quick wit and on the ball as though she had no issues at all. It can partly be a blessing not knowing or remembering what is currently going on in the world but nothing could be worse than your family members not recognising you, Therefore I think mum would have liked dementia to be the charity of choice for anyone wishing to make a donation instead of flowers or participate in the service to her memory.