There is no evidence in Maryland Marriage sources that Mary married, and no record of her death.
No Mary of John Green in Robert Barnes, Baltimore County Families.
Sources
↑ "Maryland Births and Christenings, 1650-1995," database, FamilySearch (https://familysearch.org/ark:/61903/1:1:F4Z5-MZZ : 11 February 2018), Mary Green, 02 Aug 1732; citing ST PAUL PROTESTANT EPISCOPAL CHURCH,BALTIMORE,BALTIMORE,MARYLAND; FHL microfilm 13,696.
↑ Baltimore County Families, 1659-1759, Robert Barnes, p278
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DNA Connections
It may be possible to confirm family relationships with Mary by comparing test results with other carriers of her mitochondrial DNA.
However, there are no known mtDNA test-takers in her direct maternal line.
It is likely that these autosomal DNA test-takers will share some percentage of DNA with Mary: