I don’t want to sound mean but for the sake of her remaining well being it might be a good idea to get a doctor in. If the dementia is vascular it could lead to strokes and heart problems all of which can be very painful and make her life and that of your family much worse than it already is.

It would also make sense to have an assessment of her capability for general safety reasons.
I once was called to a house where an elderly lady was trying to put a plastic electric kettle on a gas hob to boil water for her tea. Luck had it she forgot how to ignite the gas but we had to spend some time ventilating the room.