My mother was never referred to as "Mary". She was either called Mary Ruth, or just Ruth.
All of this is my personal recollection, and especially of note is her birth date, October 26, 1913, backed up by her birth certificate. Beware of references that give her date of birth as October 25. These are incorrect and come from an erroneous reading of her birth certificate that was printed in her Clinton (TN) Courier obituary, later picked up by "find a grave", and even repeated in some family trees.
It may be possible to confirm family relationships with Mary Ruth 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 DNA with Mary Ruth: