Elise
you appear to be rushed but this is only a hobby so no hurry on me. So NIcholas sailed from Derry or Londonderry if you prefer.
I looked for Campbells in the 1901 and 1911 census and there is on family in Glebe, Garadice but ages do not appear to match but head of house may be your lady's brother, one odd name in house of a daughter, Bedina, I have never heard of it. I searched only Campbell in Leitrim as putting in Garadice did not bring them back. The family are in both census.
There is a website here but they only do paid research, http://www.eneclann.ie/ but there is a podcast on DNA and Irish dimension, you can also supply an email address and get a news letter which can be interesting.
Civil records from 1864 can be obtained but you must download the form and post it in with cash in some form, they will email you a short version of the record for about $5. You will need dates though, I see now you can order online but they are showing €20 about $23 but if you do this ask for the short version, which is a photocopy from the register and is €4. http://www.hse.ie/eng/services/list/1/bdm/Certificates/
If you have isssues you can email me at this site at mailto:stpeters@irelandxo.com my actual name is Pat O'Halloran, as I keep an eye on the parts of Cavan and Leitrim you are interested in I will let you know if anything arises and I still have to meet my occassional coffee buddy whose family are from Garadice.
Finally for now I am interested a little in railways and a famous line called the Cavan Leitrim railway closed in 1959 but it passed through Bawnboy Road and the tiny station of Garadice, on page 18 of this site you can see the name of the station badly painted over the door, your ancestor probably passed through it starting on his way to the US. http://www.iol.ie/~bawnboy/index.html
Sorry but my interest in genealogy sparked an interest in social history.
Stay in touch,
Pat