yep
We go through 10 GB of data rather quickly with my sister watching movies on her IPAD at dialysis
and sometimes forgetting to switch off “cellular data” at home
Just leave the WIFI setting turned to "ON" and the iPad will switch to WIFI automatically when your home network is available. The iPad will automatically switch back to the fastest cellular connection when you leave the WIFI area. When the WIFI is operational, the cellular is not transmitting. . . and you are not using bandwidth.
Check to see if the dialysis clinic has WIFI. They should. If so, ask for the local password and use their bandwidth for the movies. The iPad will remember their password and auto-connect when you arrive for your wife's dialysis and you can stop burning your bandwidth.