Apple Watch

Depends on how she plans on using the watch.

If you need to the watch to be able to make and receive calls and send and receive messages when away from the paired iPhone, then yes, you'll likely want to get the Cellular model, and set it up with her iPhone cell carrier if they support the watch.

If it will always be near the paired iPhone, then cellular is likely not required.

See here: How to use your Apple Watch without your iPhone nearby - Apple Support

and here: Apple Watch - Carriers - Apple

If your mother had medical issues that make it imperative that she be able to make an emergency call regardless of where she is and whether or not she has her phone with her, the cellular version is what you want. Be sure to find out her carrier supports the Apple Watch.

If she has no such needs, it's a matter of personal preference and budget.