Do you have any earlier information on the name Rooney in the Manorhamilton District?
In my research, the records I have has a Mary Rooney (b. 1825 and d. aft. 1901) who married a Patrick Gallagher, possibly around 1845. They had numerous children. Their son, Patrick Gallagher Jr., b. 1853, Killargue Parish, Co. Leitrim married my maternal grandfather's sister, Alice McKiernan/McKernan, in Drumkeeran, Co. Leitrim. Alice's mother, my great grandmother, was Mary Clancy (Bryan) McKiernan/McKernan. Seeing that you have a first name of Keiran makes me wonder if all these families are all related in some way. What I know of my specific line, I have at least two of my grandfather's siblings who married Gallaghers, one of them, my great Uncle John, was a widower, and remarried another Gallagher.
Please let me know if anything here may be familiar.
Thank you.