What can I do, tax question?

My ex boyfriend's mother prepared my taxes for 2008. She has supposedly been preparing taxes for people for many years professionally, and still does it as a side job during tax season. I had divorced from my ex husband and our divorce decree/custody agreement says we claim our daughter alternating years. Well, I told her it was not my year to claim my daughter and she convinced me that it did not matter because my daughter lives with me full time. Stupidly I listened and claimed her. Now I am supposed to file a form to with the IRS and I assume I will be responsible for paying this money back?? Does anyone know how it works when you got refunded money that you were not supposed to? And what about his mother that prepared my taxes for me? She used an online service so I am not sure if her name would even be on anything..