I am not sure if you are still looking at this surname.I have a Catherine Banigan in my family hisory and the feeling is that she may have come from Donegal but there are Banigans in Tyrone (Munterevlin.) and Monaghan.
My great great grandmother was Catherine Banigan who married John Harris. John and Catherine Harris had three children Linsdsay Harris and Frederick Harris who emigrated to the US and Catherine Harris who was born about 1842-4 and who married Ross Ramage in 1870 in Limavady out of Londonderry. In 1885 Ross and Catherine Ramage moved to New Zealand.The eldest daughter who emigrated with them was my grandmother Catherine Banigan Ramage born January 1874 later Dahm.
I have had Catherin Banigan from Legaltan as a name to investigate.
I am not sure if these names are part of your fmaily.