Hi,
Thank you for your message. Sullivan is a very common name in West Cork - Have you considered contacting the Skibbereen Heritage Centre for additional assistance? http://www.skibbheritage.com/index.htm
Do you know much about Mary's emigration? The dates, the reason why she left, who she may have travelled with?..etc..Generally more information was given at the port of arrival rather than the port of departure. If you knew which city she arrived at (e.g. Liverpool, New York, etc.), this could be a good place to find more information.
Some additional sites which may be of use to you - if you haven't already tried them - are:
US National Archives/Immigration info: http://www.archives.gov/research/immigration/
The National Archives of Ireland http://www.nationalarchives.ie/genealogy1/genealogy-records/introduction/
The National Library of Ireland http://www.nli.ie/en/family-history-introduction.aspx
The National Archives UK ? genealogy search: http://www.nationalarchives.gov.uk/records/looking-for-person/
Irish Newspaper Archives: http://www.irishnewsarchive.com/
Remember to post as much information as you can with regard to the people you are researching. The more information you post, the more likely it is that one of our volunteers will be able to advise or assist you. Also include information concerning which sources you may have already used so others may further your search.
Kind regards,
Genealogy Support