Why does xfinity not offer family member setup for iwatch with cellular

Help!! Bought this new iwatch and have been on the phone for 2+ hours only to be told to go into the store. I was there for another 1.5 hours and no simple resolution. My daughter does not have a cell phone but wanted her to have a watch for gps / cellular functionality. Was told only possible for link to my phone number why?!!! Other companies offer this. Finally activated her as me but then all my texts were going to her watch. How can I just have her set up? Do I need to switch providers? Ugh!!! help!!!