I was the problem child. After many years of my mom and I getting along okay, I think she might be reverting to thinking of me as the problem child (the dementia seems to be lowering some barriers). My older brother was always the golden child, and he remains so to Mom. I usually visit Mom with my sister, who appreciates my company. I visited Mom by myself on the weekend, and she either didn't recognize me and was scared by the appearance of a "stranger" or did and thought, "cool, I can show my true feelings about you, problem child daughter."
My husband was furious. I never went back to see her alone again because she always managed to remain more civilized when someone else was present. I was an only child who never lived up to her expectations, so.....when she was cruel and ugly I never knew if it was her true feelings coming out or the dementia talking. In the end, it doesn't matter. I was disappointed in her as a mother too.
Don't go see mother alone. It's not worth the potential heartache.
P.S. My eldest was such a problem that we signed over guardianship of him to the director of a behavioral ranch program for 5 months when he was 15. It was a long 15+ years with him but he righted himself and now is a good man, partner, employer and son. However, his guilt of those years are just below his surface and it pains me and his Dad because we are very careful to never look back or dwell on them. I pray I never revert to remembering those times in our relationship. Dementia makes the sufferer say all sorts of awful and often untrue things. Choose to believe it's not real feelings so that the rest of your time together can be as good as it gets.