Did this start when he moved in with her? Does she have a family? It is possible that he thinks of her as his little girl and not the person that is caring for him. He may think of her without a family and seeing her with a family it does not fit in his brain with the little girl he "knows". In reality there is no way to know what goes on in the mind of a person with dementia. Have you or your sister asked him who he thinks she is? That might be a clue to why he does not remember her. If he thinks she is his sister from when they were younger, he could think she is his wife from when he first married, he could think .....I could go on and on but there is no way to know. As long as he is respectful to her I would not stress about it. Yes it is sad that he does not know her as a daughter. If however he begins to get violent with her, acting out sexually then it might be time to consider a Memory Care facility unless you can get caregivers in to care for him or you or your brother take him into your homes.
Any guess we could make is a guess. There is honestly no understanding the whys of memory in an elder dealing with dementia. There is so much written about the brain. Oliver Sacks made a lifelong study of this; I recommend all his books. Start with "The Man who Mistook his Wife for a Hat". Toward the end of his life he wrote more about dementia and the mind. Those suffering dementia retain long ago memories, or long term memory much longer than short term memory, so the fact that Sis is "right there" may figure in this.
My grandfather had two daughters, four granddaughters, and two sons-in-law and two grandsons. He forgot all the women and both grandsons at the end of his life and only recognized his sons-in-law.
I was visiting him in the hospital one day. My brother had gotten engaged two days before, and I didn't think my grandfather would last long enough to hear the news from my brother a few days later when he planned to visit. I said, "Papa, do you remember Tom?"
(Vague mumbling)
"He's getting married!" (Papa was also very deaf.)
His eyes popped open, he looked straight at me, and said, "WHEN DID THIS HAPPEN??"
He died two hours later, but by golly, he remembered people when it really mattered. :-)
The point is, there's no rhyme or reason as to why a mind with dementia remembers one person or forgets another. The best thing you can do is repeat my mantra -- "It is what it is."
Does she have a family?
It is possible that he thinks of her as his little girl and not the person that is caring for him.
He may think of her without a family and seeing her with a family it does not fit in his brain with the little girl he "knows".
In reality there is no way to know what goes on in the mind of a person with dementia.
Have you or your sister asked him who he thinks she is? That might be a clue to why he does not remember her. If he thinks she is his sister from when they were younger, he could think she is his wife from when he first married, he could think .....I could go on and on but there is no way to know.
As long as he is respectful to her I would not stress about it. Yes it is sad that he does not know her as a daughter.
If however he begins to get violent with her, acting out sexually then it might be time to consider a Memory Care facility unless you can get caregivers in to care for him or you or your brother take him into your homes.
I was visiting him in the hospital one day. My brother had gotten engaged two days before, and I didn't think my grandfather would last long enough to hear the news from my brother a few days later when he planned to visit. I said, "Papa, do you remember Tom?"
(Vague mumbling)
"He's getting married!" (Papa was also very deaf.)
His eyes popped open, he looked straight at me, and said, "WHEN DID THIS HAPPEN??"
He died two hours later, but by golly, he remembered people when it really mattered. :-)
The point is, there's no rhyme or reason as to why a mind with dementia remembers one person or forgets another. The best thing you can do is repeat my mantra -- "It is what it is."