« Reply #3 on: Monday 27 July 15 09:03 BST (UK) »
Have you tried the RC registers for Castlecomer now available online at registers.nli.ie? They gave baptisms from 1812. Since you have Margaret's parents names it shouldn't be too difficult to find her baptism and those of any siblings. Marriages seem to start in the 1830s, however, so there's probably no prospect of finding her parents marriage record or information on her grandparents.
O'Brien, Keogh, Byrne, Cuffe, Kelly, White, Burke, Blosset, Evans, Hetherington, Hosey, Williams, Wright, Comerford, Carey, McKeon, Litton, O'Reilly, O'Toole, Nugent, Traynor, Broughall.