It is not illegal if you are staying voluntarily. Feel free to leave if work conditions become unbearable. There are laws governing unpaid internships, however it seems as if you never came to a full agreement on what your position entailed and whether it actually qualifies as an "internship."
It is possible but it will be a longer process than usual because you will not be able to serve her with divorce papers unless a judge allows you to use publication or nail-and-mail service. If you talk with a private investigator then you may be able to locate her using the information you do know about her. Good luck!