Female ancestors are often difficult to find, particularly in records before the twentieth century, due to name changes and records based on the husband's name. Even after a husband's death, an Irish woman of earlier times was often identified through his name. I have encountered many instances, especially in Irish estate records and in ship lists from the early and mid 1800's, in which a woman was identified as "Widow," instead of by her first name. For example, I have records from the 1840's in which my Bridget Large is listed as "Widow Large" and "Widow Thomas Large." Other such women are listed in like manner. While searching an online database, I found this Bridget in Canadian records by searching for "Widow Large." (I can deduce that the result was my Bridget because of other facts on the record).
If you are searching for a female ancestor in online records, have you thought of using "widow" as a first name or as a keyword term in the search engine?