Legal Question in Credit and Debt Law in Tennessee

You can sue your daughter but whether you would be successful is somewhat doubtful. Unless there is some sort of written note or memorandum signed by her whereby she admits to the debt and agrees to pay the debt, she could easily claim in a court proceeding that your generosity was a "gift" which means that the court would rule in her favor. The burden of proof would be upon you to prove that you were essentially making a type of "loan" to your daughter by adding her to your plan, but unless this was admitted by her, you would most likely not prevail.