I know that this question seems insensitive, however I have observed a pattern in a relative that triggers my suspicion. He has non-Alzheimer's dementia. He still remembers people, places and some recent events, but has short-term memory losses, disorientation to place and time, and behavioral issues. He repeats questions often. The thing is, he seems to repeat questions much more frequently when he disagrees with the answer. I have also noticed that he repeats himself much more around people that give him his way when he persists. In other words, he acts like a spoiled kid in a toy store. Most things I have read about dementia sound like the person goes back in time in memory and that they act out the age of their last memory. Can someone with dementia remember some recent events but then behave like a child? Or, could he be mentally aware enough to intentionally take advantage of his memory loss to get his way?
I have had her tell me that she was going to "work" my sister for some information. I became leery and untrusting of her from that moment on.
Showtiming takes a great deal of effort and the person is usually very tired afterwards. Gradually the person can do it less and less and eventually cannot do it at all.
If your mother is manipulating anyone it is the medical staff, with her showtiming efforts. With you she is relaxing her efforts and her dementia is very apparent.
Who know why your mother denies you as her daughter? Perhaps she is remembering you as a child, and thinks you are an imposter. That must be very frightening for her, don't you think?
Perhaps you can go along a little. "Well, Jane, we are living together now so let's try to get along well. I am the very nice woman who is sharing my house with you, and I'll look after your needs as well as I can. I'll look after you as if you were my mother."
I hope you can give up the notion that your mother is doing this to manipulate you. She is a very confused person with dementia. She needs all the support and comfort she can get.
Has your friend's mother been diagnosed with dementia by a medical professional? How long ago? Are you a caregiver for this woman, or mostly in contact with her when visiting your friend?
People with dementia have damage to their brain. Different kinds of dementia have different kinds of damage. Vascular dementia has different damage than Alzheimer's, for example. But in all cases the damage is outside of their control. The damage is definitely not limited to memory loss.
She also does this a lot when sundowning and she thinks she has to go home. She will say, "Are you going somewhere? Are you taking me home?" I'll explain we are home. She'll laugh and say people tell her that all the time and she forgets. Then two minutes later she'll repeat, "Are you going somewhere? Are you taking me home?" I'll repeat my explanation and she'll either say she forgot or say, "Since when?" Or she'll think she needs a key to go across the street, "Do you have my key?" I ask, "What key?" She shrugs then asks, "The key to my house. Do you think it's locked?" I remind her she's home and doesn't need a key as I have already unlocked the door and then locked it to let her in earlier. She shrugs again and you can tell she's going to repeat it. Sure enough a few minutes later she's looking around, "I can't find my key. Do you have my key?" and so it goes.
Then at bed time it's always about the locks and windows. "Look that door is open! We should go close it." I remind her that's the bathroom door and I leave it open so we can find it in the middle of the night when she has to use it. She frowns then looks around trying to see out closed windows with curtains and trying to see the wall where the door used to be (we are building a fireplace where the old door used to be. We have only lived here a bit over a year so it's impressive she remembered the door being there). "That door is open." I will remind her, "Grandma there is no door it's only a wall." She will frown, "We should close it." obviously not being able to understand my words. Then she'll start back on the bathroom door until I finally get her quieted down as one of the times I repeat it sinks in.
I used to try to reword things, change the wording thinking something I was saying would sink in. I still do that thinking I'm just not saying the right words. Sometimes it works when I change it up as I think it stops the mind process from repeating but I have noticed that only works if we have already repeated it a few times. It seems to break the already in place cycle if I change it up a bit. Other times it doesn't matter how I change it, how often I repeat it or she does, the cycle continues.
Hang in there. It's not easy but it's not their fault. No one asks to have dementia so all we can do is love them anyway.