My mom is in her late 70s, has issues with dementia (though not formally diagnosed) because she is stubborn and cheap. She has signs of Narcissistic Personality Disorder and is extremely resentful of any family. She's recently told me not to be in contact with her. (I'm letting her be for a while.) But, I swear sometimes it's like I'm dealing with a very helpless and wildly imaginative (and not always in a good way) 5-year-old and other times it's like I'm dealing with a very angry, spiteful, paranoid old woman. It's very rare to have a day where it's just "mom."
It is as if her personality "unmixed" and we tend to see a different face of her each day. Some days she's extremely sad and depressed. Some days she's quiet. Some days she's chatty and joking. At this point, though, because we're not her full time caregivers anymore because she's in a facility, we're not the target of her hostility.
I agree that sometimes the adult child (or children) must step back and wait. It sounds cruel and is very hard to do, but until a person is officially diagnosed with a cognitive disorder, there's rarely anything that can legally be done.
Perhaps if you stay away for awhile, she will come around and realize - at least for a time - that she needs your help. We can hope that she does and the time frame is long enough to get her into a doctor.
If there's a true emergency, taking her to the emergency room may be a foot in the door to getting her help.
Take care of yourself and please let us know how you are doing.
Carol