INS requires a FOIA 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.
You can ask the attorney if he/she represented both parties at the same time. They should be upfront. If they are untruthful, that's malpractice.
Depending on their response, you may be concerned about a possible conflict of interest on the part of the lawyer, i.e. they representing you and her at the same time and the possible conflicts in the best interests of each party.
If you feel you are looking at a possible conflict of interest, and you want to continue, take a look at the bar association in your state. They will have public documents and statements on ethics and conflicts of interest that any lawyer admitted to the bar must follow. You may be able to ask them about what may constitute a conflict of interest, i.e. your case; or, they could refuse, saying you need to hire a lawyer for such advice.
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.