Damn that is cold! Here's what you do:
1. Change the password and email for the account.
2. Clear the account name/password from your web browser.
3. Try to log in with your girlfriend so she can see this:
"You have entered an invalid username or password. Please press the back button, enter the correct details and try again. Don't forget that the password is case sensitive. Forgotten your password? Click here!"
Even if she makes you do the lost password email thing, it will go to an email account she doesn't know about, not the original one, so for all she knows, it's closed.
This was she will trust you again, which is important, since all good relationships are based on trust.
That sounds like a good idea, going to try it!
Thanks dude!