Hi Lorraine, Taking the information that you gave us which is 100+ years old, I found Mary's 1914 birth cert on the link below. You can sign into a free account to see the cert if you do not already have it. (you may have all the links I post but I will post them just in case.)
https://civilrecords.irishgenealogy.ie/churchrecords/images/birth_returns/births_1914/01399/1575322.pdf
1901 Census http://www.census.nationalarchives.ie/pages/1901/Kerry/Tahilla/Moulcalee/1412048/ This Census shows us one of Daniel's sisters married a Sullivan and another, someone with the surname Brennan. Whenever we are looking for a family member who is missing we always look to the other lines in the family to see if the person is with them.
1901Marriage https://civilrecords.irishgenealogy.ie/churchrecords/images/marriage_returns/marriages_1901/10331/5761082.pdf
1911 Census http://www.census.nationalarchives.ie/pages/1911/Kerry/Tahilla/Maulcallee/284731/ This Census tells us that Timothy and Mary had 10 children of whom 8 are still living in 1911. Daniel & Mary Connell have Michael, Timothy, Abbey, Daniel, Patrick and Eugene, sibs of Mary born 1914. irishgenealogy.ie (civil records)will give you their births up to 1917/1918, and marriages and/or deaths until approx 1965.
Timothy Doyle died in 1916 with P. Brennan of Capparoe present https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1916/05240/4451855.pdf
Mary Doyle died 1918 with her daughter Abbey Brennan of Capparoe present https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1918/05191/4433789.pdf
Patrick Brennan & Abigail Doyle m 1897 https://civilrecords.irishgenealogy.ie/churchrecords/images/marriage_returns/marriages_1897/10466/5811512.pdf So clearly these are the parents of James Brennan age 2 in the 1901 Census visiting or living in the house of Timothy Doyle.
In terms of a potential marriage for Mary Doyle, there are 168 marriages for a Mary Doyle in Ireland available to search on irishgenealogy.ie and 916 deaths between 1936-1965.
This link gives some marriages and death records in the UK https://www.freebmd.org.uk/cgi/search.pl
If you believe Mary may have emigrated to the US this link may help https://stevemorse.org/
There are 42 results for a Mary Doyle (born 1914) in the UK in 1939 but you will need to pay a fee to open them https://www.findmypast.co.uk/search/results?datasetname=1939+register&firstname=mary&firstname_variants=true&lastname=doyle&yearofbirth=1914&yearofbirth_offset=2&keywordsplace=
All of these records are in the public domain. Also in the public domain are newspaper records at https://www.irishnewsarchive.com/
There are a number of genealogy groups on Facebook who may be able to offer you further assistance. The Kerry Family History Society is just one of them.
I do hope this is helpful to you and that you succeed in your search. Not knowing Mary's residence after 1936 will most certainly slow you down but there are many avenues still open to you.
With warm wishes
Martine