Not married -- Who is responsible for credit card debt?

In 1999 while visiting a "friend" in Long Beach, CA., I allowed this "friend" to transfer the balances of four of her high interest credit cards to my low interest credit card. At the time I had a zero balance on my card. I called the credit card company, authorized her name, Susana, to be put on the account, and then I gave them the names, account balances and account numbers of her four high interest credit cards. She and I agreed that she would pay the $12,000.00+ within a short time. I have a copy of the accounts that were transferred, and I have a copy of a letter she typed and signed (I signed as well) indicating that the balance of $12,000.00+ was her debt and that she took responsibility for it.

I have recently been cleaning up my own debt troubles and trying to pre-qualify for a home loan. I called the credit card company and was told that Susana has been late at least four times past 5 days and at least five times past 30 days. She has continued to pay the minimum balance, but has not paid off the card as we agreed. In addition, she has apparently changed her mailing address, as the credit card company told me that the last bill (Jan. 2001) was returned with no forwarding address. I told the credit card representative what had happened, and she told me that because I authorized Susana on my card and authorized the transfer of her debt from her four credit cards that I was responsible for the $12,000.00+ . At that time, I had all charges stopped to that account.

Right now I am trying to locate Susana. She lives in Long Beach, CA., and I live in Phoenix, AZ. Once I locate her, (we haven't spoken in almost a year), I will ask her to take responsibility for her debt. However, I fear she will not come through with either paying off the debt in full or paying the monthly minimum on time. As a result, my credit report is suffering.

Is there any action I can take that will remove my name from the account so that the account is solely her responsibility? Or do I need to suck up my stupid mistake and pay off her $12,000.00+ debt?