I bought a Apple watch series 7 and sold my 3.. my friend can't pair the 3 to her settings... how do I help her pair her phone with the series 3?

First, make sure you removed the Activation Lock from your series 3 watch. Follow the steps in:

What to do before you sell, give away, or trade in your Apple Watch, or buy one from someone else - Apple Support

or here are two ways to unpair your watch if you no longer have the paired iPhone:

• See the 'How to erase your Apple Watch if you don't have your iPhone' section of:

Unpair and erase your Apple Watch - Apple Support

• With a web browser, go to: https://www.iCloud.com and sign in with your Apple ID. Open Find My iPhone and select All Devices (at the top). Then click your Apple Watch, select 'Erase Apple Watch', and select Next until the device is erased. Finally click "X" next to remove your Apple Watch.

Next, she should follow the steps in:

Set up your Apple Watch - Apple Support

FWIW (especially with a series 3 watch), you may also want to see the replies to:

Apple Watch 3 is stuck on preparing updat… - Apple Community