You need to change the primary account to a local account. Log off then log in again then change the local account back to a Microsoft account using your wife's live email and password.
Full instructions here, see answer on second post.
Before you do that I suggest that you create another local account first. Log in to the PC, go to users, create a local account and name it Maintenance or some such name. Make sure it is an administrator account and give it a password. This is puerly a backup in case you can't log in to Windows 8 some day on the primary account.