Your Post very definitely caught my interest. I have been researching the families of the Carna parish for 15 years.
Firstly, I looked at the 28 Nov 1884 Boston marriage of Thomas Cooney & Ellen Connolly. Ellen's parents are shown to be Patrick & Sarah. I have only one family that fit this criteria: that of Patrick Conneely & Sarah Conneely who were having children in the 1850s and 1860s. For the most part, the family lived in the section of the Kilkieran townland named Bontroughard.
The odd thing is that I could find no daughter Ellen in the records for this family. And I even rechecked with the Galway West Family History Center on that. But I do have a daughter Evelyn in my data who was baptized 02 Oct 1856. In all my years of researching the parish, I have never before or since come across the name Evelyn in any other family. I mention this because I wonder at the possibility that this Evelyn is actually your Ellen - the wife of Thomas Cooney.
The 6 year birth difference (your 1862 vs my 1856) should not be considered a major impediment to my theory. Most folks born in western Ireland at that time had no real idea of how old they were. Years of research have shown that most folks estimate their age to be about 5 or so years younger than they really are.
Just passed along for information, but I would be happy to hear your thoughts. It may be easier to communicate with me directly by e-mail. My e-address is email@example.com
Portsmouth, Rhode Island