They can still request a doctor's certification as to your wife's condition.
If you didn't provide one then it is going to make your case more difficult but since they never discussed your rights you at least have an argument.
You have to start by filing a complaint with the Department of Labor. The website for that is at https://www.dol.gov/wecanhelp/howtofilecomplaint.htm
They will investigate and then either enter an order or tell you that you can sue.
You may want to visit with a local lawyer that does employment law, you can find one at www.lawyers.com, in the section for Area of Practice enter Employment Law. If they are interested in representing you they may want to look over any papers you send to the Department of Labor.
If your question has been answered then I'd offer my best wishes to you and ask that you please not forget to leave a Positive Rating so I receive credit for my work.
Of course, please feel free to ask any follow up questions in this thread. I want to be sure that all of your questions are answered. In addition, once you issue your Positive Rating the question will lock open and no longer time out so you can come back to it anytime in the future if you think of any follow ups.