Hi Pauline,
Thank you for your message. I hope that someone with information gets in touch.
In the meantime,I found a record of a Mary Renehan, Dundalk, 1854:
http://www.askaboutireland.ie/griffith-valuation/index.xml?action=doNameSearch&Submit.x=0&Submit.y=0&Submit=Submit&familyname=Renehan&firstname=First+Name&baronyname=&countyname=LOUTH&unionname=
You could also try looking at church records. Most Catholic records are held locally so you may need to write to the local parish priest for possible assistance. One website that you may find useful is the Irish Times where they give an overview of what records are available in specific parishes. It also shows you where copies of the records are available. For Dundalk parish, follow this link:
http://www.irishtimes.com/ancestor/fuses/rcparishmaps/index.cfm?fuseaction=showidrecords&CityCounty=Louth&parish=Dundalk&churchid=216
Some other websites that you may find useful are:
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
Irish Genealogy Tool kit: http://www.irish-genealogy-toolkit.com/
Genealogy Links: http://www.genealogylinks.net/uk/ireland/louth/index.html
From Ireland: www.from-ireland.net
KInd regards,
Genealogy Support