Usually this notification comes up when a device location feature is used, such as is available with a Google or Samsung account. If you never wiped the device after removing her accounts it's possible she's logging in to her Samsung or google account and using that feature.
You would, however, need her help to remove those accounts as the password is needed, and you MUST remove them prior to resetting the phone so simply doing that won't do you any good as you'd need her to set it back up and you still haven't resolved that issue as the account(s) would be back on the phone.
12-17-2020 10:33 AM