Q u o t e:
From http://us.battle.net/faq/index.html
Q: My family plays World of Warcraft together. Should we create a single Battle.net account for all of our World of Warcraft accounts?\
A: No. Sharing access to a World of Warcraft account, other than by a parent or guardian with a single minor, is a violation of World of Warcraft’s Terms of Use. You should create a separate Battle.net account for each family member’s World of Warcraft account. In addition, future Battle.net features will make it beneficial for players to have the Battle.net account they use associated with their own online identity. Creating separate accounts for you and your family ensures you will be able to take advantage of these features when they are introduced later on.
Your girlfriend, unless you are her legal guardian, has been using that account in violation of the Terms of Use. That account is in risk of account actions, up to and including account closure.
However, when you have multiple accounts under one battle.net account, you get an additional dropdown menu or a new selection screen to choose which account to log into at the game login screen.
