Hi Raygan, welcome to the forum. I am very sorry to hear about your Nan. I think most of us here, if not all, know someone, who has had or have a Family member, or one of their own Family suffering from this dreadful condition.
My best friend's Mother had it & my friend said it was her Mum sat in the chair, looking at her, but the person she was/had been, had vanished, so I do know what you mean.
It is horrible for the other people in the Family to go through.