Cannot print from Mac Sierra to Canon 7550

A question on behalf of my Swiss neighbour She has a MacBook Pro (Retina, 15-inch, Mid 2015) running Sierra, and a Canon 7550 printer (MG7500 series). - WiFi router is configured on Macbook (browsing works fine). - The printer (Canon 7550) is configured on the MacBook, with the correct print driver version installed and a little green circle showing beside it's name (suggesting the installation is good). - The printer IP address is configured (listed) on the WiFi router. Nevertheless, every time a print job is started, we get the message: in German: "Drucken - Der Drucker reagiert nicht" (English equivalent: "Print: The printer is not responding"). Despite a superficially correct end-to-end configuration, the Mac doesn't seem to "see" the Canon 7550. It also fails to "see" the printer using a direct USB cable connection, and using Airprint. Strange is that my neighbour went to a friend with her MacBook, and could print to her neighbour's Canon printer with no problem. We've deleted and (in all but results) correctly reconfigured everything quite a few times - to no effect. Would be grateful for a couple of further troubleshooting suggestions or tweaks. Tks