If it appears there was a conflict on interest and you want to continue, you need to find who administers the disciplinary committee for lawyers in your state. That will be either the state bar, a committee under the state government or a committee under the state supreme court. They have the power to discipline lawyers, ranging from from fines to disbarment. You can ask them about the process to file a complaint.
For any formal complaint, you will need to show harm to yourself, as in it cost more money for the divorce to be finalized, or some other tangible issue.
INS requires a FOI A https://www.foia.gov/ for immigration status information. But if her case was in a public court, that information - including who represented her - would be available.