Safety tap

My wife has dementia. She likes taking baths. One day she nearly scalded herself by emptying the bath while still in it, replacing the plug and turning the hot water tap fully on. She then panicked and neither turned off the water, nor got herself out of the bath.
For the next few days I agonised over what to do. I investigated thermostatically controlled taps but the cost of all the required parts was estimated at approx $2,000 with installation on top.
In the end I thought of dis-assemblin