1901, mother Anne is Catholic.
http://www.census.nationalarchives.ie/pages/1901/Limerick/Garrane/Knocknagranshy/1489185/
Is this the family?
Annie was already a widow in 1901. Both sons, aged 22 and 17 were C. of I. as was elder daughter, Katie (19) and a servant. Younger daughter, Annie, aged 14 was R.C. I guess that father was C. of I. If he died in younger daughter's early childhood, mother may have had more influence over younger daughter's religious upbringing. On the other hand the parents may have decided that the girls would be Catholic but elder daughter preferred otherwise. As well as searching for baptisms of the girls as babies, look for possible later baptisms.
"The role of Ne Temere in the decline of an Irish custom regarding the religious affiliation of the children of mixed marriages" by Jesse Buck sets out the argument that the 1908 promulgation of "Ne Temere" the Papal decree on marriage led to a decline in mixed marriages and in the custom of sons of those marriages following the father's religious affiliation and daughters, that of the mother.
The custom may have been in part a remnant of penal laws when Catholics were discriminated against when it came to land ownership, inheritance and professional life.
One study I read showed that children of a mixed marriage were more likely to be R.C. if the mother was Catholic. (I can't recall name of the study or dates.)
