Where to apply for Indian Nationality Certificate in Navi Mumbai.?

My wife born in nepal but living in Mumbai for last 24 years with her parents. She has ration card, voter id card, pan card etc. But for issuing pport, authorities are asking for nationality certificate. I am an indian citizen. We have got married for 4 years. Now we are staying in Navi Mumbai. Can anyone suggets how to get indian nationality certificate for her and where to apply for.