There is a lot of debate about “therapeutic fibbing”—the idea of choosing not to tell someone with dementia the truth as a way to handle a situation that is causing them to be upset.
It is best to try another technique first, and then to use therapeutic fibbing if other things fail.
So, in this case, you might try redirecting your loved one by asking him or her to tell you about her relationship with “this person”, why “this person” is important to him or her, or to tell stories that you know about your loved one and “this person’s” relationship. If that doesn’t distract him or her or give her comfort, you certainly can try telling her you are “this person”.
With dementia, people aren’t able to retain the “facts” and we can’t talk the out of dementia. The goal is a good quality of life for everyone. So, in some circumstances it can be beneficial to them and to their caregivers to not tell the truth fully.
The important thing with this technique is to make sure you aren’t robbing the person of the full human experience or to protect them from having emotions that we all have. Instead it is about doing what is kind and contributes to their quality of life.