I have been researching my Irish roots for 25+ years, and it has been my experience that it was very common for women to change their names and especially their birthdates. It seems that they changed their ages to suit the situation. Several of my female ancestors changed their ages to be younger as they got older. Whether this was because they actually forgot their real ages, or whether they were being vain, I don't know.
My great grandmother was born Bridget, a very common Irish name, and showed in 1900 as Bridget on the census in Chicago, but in 1910, after the death of her husband, was listed as Annie. My mother said she remembered calling her grandmother Annie.
In reading Irish records, it is clear that women had nicknames that were often used in place of the real name.
I have used rootsireland.ie for a lot of my research on my Roman Catholic ancestors. It is a paid service, but you can subscribe by the month. Their records are often attached to copies of the microfilmed parish registers which you can view. However, the registers are written in Latin and are very difficult to read.
For Protestants or others, try the Public Records Office for Northern Ireland. You can google PRONI to get the link.
Ancestry.com has Irish records now, but I have not spent much time looking at them as I am trying to get away from using them.