If your mother is having the document notarized, write it in her voice. “My name is Jane Doe. I was married to John Doe on XXX but we have been separated since XXX. I moved with my child, Little Jane, to this address on XXX. John has never lived here. To the best of my knowledge he lives in ___ but I have no contact with him. He provides no support for Little Jane.”
Just pack it full of whatever info your mother knows.