All iPad models are available in two versions - namely WiFi Only, and WiFi+Cellular. The WiFi+Cellular models principally differ from WiFi Only in that the former can be used independently of WiFi - whereas the using whereas the WiFi Only model can only access the internet using an available WiFi Connection.
However, if you also have an iPhone, a WiFi Only iPad can use the iPhone's Cellular hotspot feature to access the internet when away from a WiFi network.
If your Mom already has an internet connection at home with WiFi, then a WiFi Only iPad might be adequate for her needs - while the iPhone can be useful on its own when away from home, or in providing a Cellular connection for the iPad if needed.
The other significant difference between WiFi Only and WiFi+Cellular models of iPad is GNSS/GPS functionality - this feature, providing accurate location services to the iPad, is only available on WiFi+Cellular models of iPad.