This will work if your wife hasn't accessed the admin account.
Boot laptop and press and hold F8, then use the arrow keys to select "safe mode" this will not require a password.
Once booted, select start, then run, Now type the following command:
net user administrator /active:yes
restart the laptop normally and the hidden admin account is now active without the need for a password. You can then use the admin account to change your wife's password. Once done I'd suggest turning off the admin account, type: net user administrator /active:no into the run box to do this.