Les:
I searches the subscription site Roots Ireland and located a September 21 1838 baptismal record in the Killanummery RC church. Parents were Owen Kelly and Anne Kelly. No sponsors shown. Usually the mother's maiden name was shown so Anne may have been born Kelly. Other siblings were Thomas 1836 James 1841 Patrick 1843 Michael 1845. All records showed Anne Kelly for the mother
The parents were married April 30 1835 in Killanummery. Anne Kelly was the bride
The 1857 Griffiths Valuation head of household listing showed two Owen Kelly records in Killanummery civil parish. One in Garvagh townland and the other in Greaghnafarna townland. One of the two would be your ancestor. https://www.failteromhat.com/griffiths/leitrim/killanummery.htm
I also located a August 7 1846 baptismal record for a Margaret Costelloe with father Michael Costelloe and mother Judith Couny. Judith and Johanna were sometimes used interchangebly. The RC parish was Ogonnelloe and they lived in Carrowbawn.
If this is the correct family then the parents had the following children in addition to Margaret although at least two appeared to die young. Mary 1844 Mary 1848 Catherine 1854 John 1855 Mary 1857 Timothy 1859 Joan 1861.
I did not locate a marriage record.
I looked at the 1855 Griffiths Valuation head of household listing for Ogonnelloe civil parish and there was a Michael Costelloe in Ballynagleragh townland. Likely Carrowbawn was a local placename and the official name of the townland was Ballynagleragh.
https://www.failteromhat.com/griffiths/clare/ogonnelloe.htm
Let me know what questions you have.
Roger McDonnell