Unfortunately, we don't have a parish liaison in that area of Co. Cork. I will check with our HQ becasue I know we are adding more volunteers in Cork.
A couple comments. I did not find a church marriage record on Roots Ireland in Castlelyons so I suspect she did not marry. Possibly she emigrated, died young or was a spinster.
Did you find a townland name in any of the records you found in Castlelyons.
Civil registration started in 1864 for BDMs so if John died before 1851, the only possible record would be one kept by the church and the Castlelyons register does not show death info.
Have you considered autosomal DNA testing?
I checked the 1901 census and there were two Coughlan families in the area around Castlelyons. Possibly there is a connection with your family.