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The 1855 Griffiths Valuation head of household listing for Kilgefin civil parish shows many Dowling records. If Mary left Ireland after 1855 then the Mary Dowling shown in this listing is likely her. There is no way of determining the relationship of the other Dowlings in Cloonageeragh. The RC parish records do not start until 1865 http://registers.nli.ie/parishes/0540
The 1901 census for Cloonageeragh http://census.nationalarchives.ie/pages/1901/Roscommon/Drumdaff/Cloonage... shows three Dowling families.
The online Irish phone book only shows one Dowling entry in Co. Roscommon and the person lives near Athlone.
You may want to consider autosomal DNA testing.