Have you gotten a copy of Maggie's marriage and death records? Either one may have data on her parents. The cemetery may have something in their burial records that maybe helpful. If she was Catholic check with the Archdiocese for church records on her birth, marriage and death. When Alonzo was christened her relatives may have been the godparents. More than likely the Archdiocese has an archives they will direct you to. It's not likely her obituary will mention much, it may be little more than a death notice, but you never know. The New York City Library may be able to help. You could also try the New York City Municipal Archives to see if they can help you especially in getting her death record.
McElmoyle does not appear in the census for New York. It could be a spelling problem or she wasn't born in New York despite what the 1900 census shows (which does show her parents as born in Ireland).