Legal Question in Immigration Law in District of Columbia

I am not fully clear on your situation, but if your mother entered on a valid visa and then overstayed you can file an immigrant visa and adjustment application on her behalf. I strongly suggest you privately consult with an immigration attorney to review all the details before you file anything.

You need to clarify the facts of your situation. If I understand your question correctly you are actually asking two question. First, whether you are a U.S. citizen based on your birth in the U.S. even though your mother worked in the Nigerian Embassy. Second, if you are a citizen, whether you can sponsor your mother.

As to the first question, if your mother was a diplomatic-level employee of Nigeria at the time you were born, you would not be a U.S. citizen based on your birth in the United States because the children of foreign diplomats are not subject to the jurisdiction of the United States. If your mother was not a diplomatic-level employee the exception to the principle of citizenship for foreign diplomats would not apply to you, and you would be a U.S. citizen because of your birth in the U.S.

As to the second question, you should be able to file an immigrant visa for your mother as an immediate relative if you are at least 21 years of age, assuming there are no other issues or problems. As the answer above correctly states, you should consult with an attorney before you file anything.