Apple Watch Fall Detection and Cellular

I'm purchasing an Apple watch for my 80 yo mom because of the Fall Detection. She has an iPhone that I will sync with her Apple watch. If her Apple watch only has GPS, will Fall Detection only work if her iPhone is nearby?

I'm worried that she might travel somewhere and forget to bring her iPhone and fall. Should I get her an Apple watch with both GPS & cellular? I'd want Fall Detection to work regardless if her iPhone is nearby or not.

Thank you.