You’re most welcome! I still want to try and help, so I’ll share some ideas for what you could do.
Obviously, reverting to W10 is a strong idea. If you can pay for the extended support, I’d suggest to try that too. It is a bit expensive, but nonetheless worth it if you value your privacy as much.
During this interval, a good idea would be to see if your wife can get used to Linux. You could set up a VM for her, install Linux Mint (it’s perfect for transitioning from Windows) and assist her in getting used to it. At one point, if your wife feels confident in making the switch, you could always go ahead and dual boot LM on her PC so that she has both OSes available.
Since you did say that it’s a no-go territory 
, there is one more option which might require some work on your end. You could install Safing Portmaster and use it’s firewall functionality to restrict internet access for the Recall feature. Now given that we don’t know how exactly Recall and CoPilot will be integrated into the system, there is a chance it will be bundled with some system apps and therefore disabling internet access would affect those utilities too. Nonetheless, it’s worth a try!
Or, at the absolute last bet, you can get your wife a Mac.
Hope that this was of some value!