Why does my mom think I’m an imposter of her real daughter?

...research shows that it�s more common among people with neurodegenerative conditions such as dementia; up to 16% of those with Lewy body dementia or Alzheimer�s also have Capgras syndrome. Source: https://www.webmd.com/mental-health/impostor-syndrome-capgras

Search Capgras Syndrome to n your favorite search engine and on AgingCare. Plenty abounds about this dementia related delusions.

Please get as much education as possible regarding your mom's dementia. Her brain, if you could see it, may look a bit like swiss cheese if you will. There are all sorts of things missing that allow a normal brain to have memory, to retain information. For your Mom that's missing.

I would start with some Teepa Snow videos. Oliver Sacks is also easy to read and entertaining while he explains the many ways that the brain can "get it all wrong" whether by dementia or injury.

I wish you the best. It's a steep learning curve for families.