Hello and thank you for contacting us. This is Dwayne B. and I’m an expert here and looking forward to assisting you today. If at any point any of my answers aren’t clear please don’t hesitate to ask for clarification. Also, I can only answer the questions you specifically ask and based on the facts that you give so please be sure that you ask the questions you want to ask and provide all necessary facts.
No, you can't sue for "confusing interest rates". There are possible causes of action depending on exactly what happened and how. For instance, if they are charging more than the law allows then there is a cause of action for what is known as usury. If they somehow misled your wife as to the interest rate, for example they told her 7% and then changed it to 12% after she signed the papers then there would be a cause of action for fraud.
However, if your wife actually was the one that signed the papers then the cause of action is probably going to be hers and if she signed the papers in 2013 the only statute of limitations that would allow her to pursue a case in Texas is one for breach of contract which has a four year statute of limitations. All of the others which might apply have a two year statute of limitations.
If she thinks she has a case then she would want to take all of the paperwork, including any letters or emails, to a local lawyer who does Civil Litigation (she can find one at www.lawyers.com) and let them review the paperwork as well as do an extensive interview and investigation.
Please feel free to ask any follow up questions in this thread.