It is not clear what you are trying to do. But
- go to https://account.microsoft.com/devices/store and remove the device
- go to https://account.microsoft.com/devices/ and remove the device
- go to https://myservice.surface.com/en-US/pages/managedevice.aspx and remove so that you wife can register it under her Microsoft ID
- make sure her Microsoft account/ID on the tablet is an administrator account
- log off your ID and login to her ID and remove your account from the Surface
or you can completely reset the Surface instead of 4 and 5 and set up fresh for her account.