Credit one bank Bad customer support. Got a card for my gf and I and it destroyed her credit for me using the card and she never used it. I am the primary so why should it affect hers. Las Vegas Nevada

When you put your GF on your account, she gets ALL of the history of the card. You don't get to pick and choose what gets reported.  So yes, if you use the card it is the same account so it gets recorded on her credit as it being used.  Just like if you failed to pay and become delinquent, it would show as delinquent on her credit. 

By the way, if you put your GF on your account how come she didn't know about it?  You should have asked her BEFORE you did this if she wanted to be on the account, at the very least told her that you were going to do this.  Depending on what information you gave them you may actually have committed Identity Theft.  Where if you ever broke up(and with what you did that is a very likely possibility) she could turn around and have you ARRESTED, or at the very least sue you for any financial harm you caused by YOU destroying her credit.   Yes it is that serious.

You can try to remove her as a user, and then have her dispute the line on her credit.  But your real issue isn't with the bank, it is a personal one between you and your girlfriend.  Where the only way to resolve this is for you to "man up" and be 100% honest with her.  Good Luck...You are going to need it.