Roots Ireland - www.rootsireland.ie - Subscription Site - has a record of a "Margaret Kenefick" for October 28th 1843. No record for October 4th 1843.
There are eight "Margaret Kenefick" with various spellings recorded fotr the years 1838 to 1845 inclusive in County Cork.
Do you have her parents names? You should check her marriage and death certificates for their names.