Shutdown on lid close or sleep external boot device

[fredfrog]

My daughter's macbook air has a broken internal ssd - it no longer works and is not visible. The rest of the machine is fine. Replacing the SSD is too expensive. I can boot it and run perfectly fine from a USB stick without any internal SSD storage and am running Catalina on it. With a USB 3 stick its plenty fast enough. However, to prevent her from sleeping the device I'd like to set it up so that it shuts down (to complete cold state) on lid close. Of course starting will require the usual button press after opening the lid. How can I do this ?

Alternatively, how can the USB stick be handled when the laptop sleeps ? So far sleeping the laptop causes a crash on subsequent startup - presumably because power is withdrawn from the stick and it doesn't start again in the same state.

Thanks for all advice.

andy