Sync ipad to apple watch

I am allowing my granddaughter to borrow my ipad Air.

I want to unsync the ipad from my iphone and instead sync the ipad to her apple watch phone number.

Her apple phone is not under my account its under her mother's account.

Is this something i can do without having to transfer any monthly fees to her or her mothers' account? I still will own the ipad as its just a loaner for now. And more importantly is is possible to sync an ipad with an apple watch? Thank you