You can't do that, but you can set up an Apple Watch with your phone for her to use. See Set up an Apple Watch for a family member.
From the site:
How it works
With Family Setup, your family member who doesn't have their own iPhone can use their Apple Watch to do things like make phone calls, send messages, and share their location with you.
After you set up a watch for a family member, you can use your iPhone to manage some of the watch's capabilities.
Note that some Apple Watch features depend on having a companion iPhone, and aren't available on an Apple Watch that you pair using Family Setup.