Sailing Away with Emily

     My third great-grandmother, Emily, on my maternal grandmother's side was born in Ireland.  If the Emily Devine I found in the 1900 U.S. Federal Census is my Emily then I know that she was born in 1846 and arrived in the United States in 1851, if the census information is correct.
     Emily's maiden name was Sheldon.  I have verified this with her daughter, Teresa's baptismal certificate.  Teresa Devine was my great-great-grandmother.  The certificate has Mary L. Sheldon listed as the sponsor.  If I had to guess, I would say that Mary was Emily's sister.
     I checked the New York ship passenger lists for an Emily Sheldon born in 1846 in Ireland.  The only record I found was for an Emily Sheldon born in 1851 and listed with J. Sheldon, Mrs J. Sheldon and Mary Sheldon who was two years younger than Emily.  This Sheldon family is listed as American and the arrival date is 1857 on a ship named Vanderbilt.  I have not found any other Emily Sheldon born in Ireland in or near 1846.
     I checked the census records for Emily and her family.  The Sheldons that I found were all born in New York.  I found an Emily Sheldon born in 1846 with a younger sister named Mary who was born two years after Emily.  These Sheldons lived in Canaan, NY which is in Columbia county.  I don't see how this could be my Emily when every census I checked for this family showed place of birth as New York.
     Emily Sheldon was six years old when she arrived in this country according to the New York Ship Passenger Lists and the U.S. Census.  Although both records have a different date of birth, the arrival date is six years later on each record.  Emily met and married a man named Patrick Devine and they lived in Stuyvesant Falls where my 2nd great-grandmother, Teresa was born.  Stuyvesant Falls is about 23 miles from Canaan in a southwesterly direction.
     How odd that there was an Emily born in 1846 with a sister named Mary and living in Canaan as a girl and years later my Emily, married was living in a town not too far away.  Is this Emily one and the same person or am I looking at two different women?
     My great-great-grandmother Teresa's death certificate has her mother, Emily's place of birth as Ireland.  The 1900 census also shows that she was born in Ireland and I'm sure that Emily, being the informant would know where and when she was born.  The passenger list has her date of birth as 1851.  I thought maybe the census taker had made an error in the dates and put the year of arrival as 1851 instead of year of birth but the passenger list had her nationality as American.  Then I took another look at the different censuses for the Sheldon family and thought, well, maybe...  since the 1900 census had her year of birth as 1846 as well as these censuses, it might be possible that this is my Emily?  but, again this family is American and the head of household is Fenner Sheldon, not a Mr J Sheldon as listed on the passenger list.  Emily and Mary are two years apart on the censuses as well as the passenger list.  I know that Emily Devine sailed over from Ireland but I have no documentation.
    
     Searching for Emily is making me want to jump ship...