The problem is, node-red (including cron-plus) work at the server side. The browser is 100% client side.
You could, as suggested, trigger a shell script IF node-red is on same machine as browser....
Cron-plus > exec shell > (opens browser)
Uicontrol (detect connection to dashboard) > exec shell (to take screen grap and save to file. Then, close browser)
Uicontrol (detect browser disconnected from dashboard) > load file > email it.
Just a whole load of hassle.
There are probably tons of scripts or apps that can fire up a browser and print to image on regular schedule, then you can just do this...
Cron-plus > read file > email.
