The principal is my daughter and I'm an authorized user. I closed my account several years ago but my daughter accumulated over $7000 without my knowledge. When I pulled my credit report I was shocked to see her balance reflected on mine, affecting my credit score.
1. Am I also legally responsible for her unpaid balance?
2. How bad will it affect my credit score?
3. How can I get out of this mess?
I have always been responsible and it's sad that I am affected by the irresponsible acts of my daughter. Please advise.

Are you an authorized user or a joint cardholder? There is a big difference.

If you are just an authorized user, it shouldn't be affecting your credit. Many places do not have authroized users anymore. As a joint cardholder, you are as liable for the debt as your daughter.