My mother insisted that because her bath water was cold she needed a new water heater. I called the plumber who had been at our home before. When he was there before he fixed two of three toilets. It seemed the heater problem was not a plumbing issue but a mother issue. My mom told him to replace the heater then began to insult him. I told her to stop but she continued. As he left she refused to pay him for the visit. I sent an email apology to the plumbing company. What in the world happened here? Is this dementia?
For a while, why don't you run her water for her and see for yourself whether or not there is an issue. Use a thermometer to check the temperature.
My question is how long was she sitting in that cold water getting chilled before she began complaining? Perhaps she was so chilled she became angry and even more frustrated.
Dementia can show up in small ways that we don't recognize at first. Some are as simple as placing trash in odd places or lying about things. Personalities may change as well and they become hostile or withdrawn. I might check these things out before she has access to large sums of money, just in case.
I'm more curious about YOUR behavior, frankly. The guy must have thought he'd bought a ticket to the loony bin.