Identity of Bridget Cummins

We know very little about my great-great-grandfather's (Thomas Cummins) family. According to the 1901 Irish Census he was born in Tipperary, but I have not been able to figure out who either of his parents might have been or whether he had any siblings.We can first pinpoint him in Tullamore, where he married and had all of his children. He took the entire family to Breaffy, Castlebar, Mayo in about 1874 with the exception of his eldest son, Michael Bernard (born 1863). 

Michael married Mary Molloy in Dublin and had his first child, Mary Elizabeth there in 1887. His other two children, Thomas Bernard (1889) and Christina (1890), were born in Tullamore. On both Christina's civil birth record and civil death record, a Bridget Cummins was in attendance. On Christina's death record Bridget is referred to as her "Grand Aunt." If that label is accurate, Bridget had to either have been a spinster and was my great-great-grandfather's sister or was married to my great-great-grandfather's brother. Other than that 2 1/2 year period, we have no knowledge of where she came from, who she was, or where she went afterwards.

If there are still Cumminses in or around the Tullamore area who might be related to my Cummins "mystery woman" I would appreciate the help in knowing moer about her.