New mixer tap for instantaneous water heaters

Hello dear plumbing experts,
maybe someone here can give me a tip, it’s about the shower fitting of my 87-year-old neighbor. As can be seen in the pictures, the current fitting hangs centrally on a 1/2" wall flange (cold water). The instant water heater is connected directly to the faucet with two hoses. Beautiful!
Why do I want to change this? Because the neighbor either freezes or scalds herself and fiddles around with both taps and the power regulator of the instant water heater for minutes until the temperature finally fits. Not a nice situation, at 87 you don’t have much time left for such things, the clock is ticking...
Now I have little experience with such crappy instant water heaters. My question:
Can I remove the old tap, install a T-piece, and permanently pressurize the instant water heater on the cold water side and go directly from the hot water side of the instant water heater to the "hot" side of a modern mixer tap?
I couldn’t find modern taps with "direct" connections for the instant water heater... probably never caught on...
Greetings from Lower Saxony
Chris

Hi Chris

The hydraulically controlled instantaneous water heater won’t work.
If I’m not mistaken, the modernization should also cost as little as possible?
I would go for, for example, a DHE 18 - 24 from Stiebel Eltron.

Olli

Hello Olli,
thank you very much for the feedback and the information. I had already suspected that the old instantaneous water heater would not be "compatible."
However, the old lady has meanwhile decided to leave the installation as it is for now.
Best regards
Chris