My mum at 69 went from a vibrant intelligent loving woman to the wicked witch from the West in a very short time.
Be thankful that your mothers/relatives are only verbally dodgy and sometimes repetitive although that can drive you up the walls too.
Mum, without anyone knowing as she never went near doctors except for her flu jab and check over once a year, had been having TIAs and was developing vascular dementia. I'm telling you, no word of a lie that when I took her out for lunch, on more than one occasion I had pots of tea thrown at me, chairs upended, shouting, the works. It was awful both for her and for me as I doubt she had a clue what her behaviour was like. I think of it as frustration. She could not remember everything she thought she could, she was also frightened by it all.
I really knew things were bad when the "handbag" syndrome started. That's where her whole world revolved around her handbag. And her purse, counting and re counting her money, thinking everyone was stealing from her, screaming at potential strangers (thieves). When I think back on it.....
My siblings and I took turns to look after her by using sabbaticals, leave of absence and shorter hours etc. I will never regret that, but it was bloody tough. Mum eventually needed full time care, and surprisingly was very happy in her new home as she said she was now "the boss" and could tell the staff what to do. They knew how to deal with such things brilliantly.
I am sorry for the essay, but I wish you well. In your case it could be just boredom and a shrinking world, but keep an eye on it and keep in the loop with her GP. I wish you and your mum well.