PC unable to see Mac Desktop while logged in

Howdy,

For years, our bookkeeper has logged into our headless remote Mac Mini (running Sierra) here at the house to take care of QuickBooks reconciling and so forth.  She has a paid account and one seat for us. A few months ago, the hard drive in that died, a new one was installed, and we did a fresh install of Catalina, the latest OS.  After a few display resolution bugs I sorted out, we got it back to normal, installed QB 2019, and have accessed it easily enough using Apple Remote Desktop on the same network.

A few days ago, our bookkeeper sent us the LogMeIn invite and I clicked the link and installed the LogMeIn control panel (64bit version 4.1xxxxxxx) and thought we were good to go.

The problem is that while she can log in to the computer, the actual desktop is blacked out.  She can see my mouse arrow skate across the blackness, the program I'm in at the top of the screen, but none of the application windows that hover over our desktop.  I tried different monitor resolution settings, I turned off the firewall (never a problem before), and uninstalled and reinstalled the LogMeIn client and control panel to no effect.  I’ve never seen a remote access get halfway like this before, so I’m stumped.  

If anyone has any ideas of things I haven’t tried, I’d be grateful.  We just never had this issue before with the older OS, but otherwise, it’s the same 2 computers trying to connect.

Much obliged,

Mick