Catherine McCarthy is not on the main line of descent through Dennis, Justin and Dennis (see will extracts below). The side branches don't offer much either: if the French are to be believed:
"1. Jacques Mac-Carthy, mort célibataire ;
2. Justin, dont l'article suit ;
3. Charles Mac-Carthy de Laganstown , dans le comté de Tipperary, marié avec Clara O'Farrell, mort sans postérité ;
4. Denis Mac-Carthy, marié avec N. Herringman, mort Londres sans postérité ;
5. Alexandre Mac-Carthy de Bartletts Buildings å Londres, mort célibataire"
Dennis McCarthy of Spring House (?-1713) left children James, Justin, Charles, Dennis, Alexander, Daniel(?), Elizabeth, Joan, Margaret, Catherine, and Mrs Fox (Honoria) - https://www.familysearch.org/ark:/61903/3:1:3QS7-L9LW-6CJB?cat=224404 Not mentioned is Maria who married Daniel Mahony of Dunloe and died in 1739.
Justin (1685-1756) left children John, Dennis, Margaret & Elizabeth -
https://www.familysearch.org/ark:/61903/3:1:3QS7-L9LW-6CYT?i=910&cat=224404
First son Dennis (1718-1761) only names son Justin in his will - https://www.familysearch.org/ark:/61903/3:1:3QS7-L9LW-6CYT?cat=224404
Second son John (1725-1788) supposedly had 4 sons and 4 daughters. He died intestate, daughter Elizabeth is appointed administratrix - https://www.familysearch.org/ark:/61903/3:1:3QS7-99LW-2VNT?cat=224404