Watch fall detection without iPhone.

No, you cannot pair an Watch with an iPad.

But if you have an iPhone then you can buy your mum an Watch Series 6 and then configure for her with your iPhone.

Read here => Set up a family member’s Apple Watch - Apple Support

Yes, to use an activate an Apple watch you have to have an iPhone even with a cellular watch. If she keeps her phone nearby she doesn't need cellular for her watch. That is what I do as I also bought mine for fall detection. The cellular is good in case she goes somewhere and forgets her phone then fall detection works anywhere. Cellular watch usually adds ten or fifteen dollars to your cellular plan in USA. If you hook her watch to the family plan instead of her own iPhone be sure to get the cellular watch then she is covered even if you’re not there.

You're welcome.