Mary's birth name is either Clark or McIntyre:

In Mary's first marriage, on Jan. 25, 1894 in Boston, MA, to Joel O. Cobb, her information is:
Mary E. McIntire, 24, at home, b Grafton, MA, res. Lynn, MA, Patrick and Susan McIntire, parents.
Joel O. Cobb, 44, Shoemaker, b Grafton, MA, res. Lynn, MA, Joel F. and Abigail Cobb, parents.

Son, Walter Arnold Cobb, b Feb. 1, 1890 in Chelsea, MA. Walter's birth preceeds his parents' marriage.

Joel and Mary divorce, as evidenced by Mary's second marriage, information below.

Mary married Frank E. Noyes. 26 August 1903, Lewiston, Androscoggin, Maine.
He was 48 years old, employed in the leather business, widowed, 4th marriage.
She was 31 years old, b Lynn, MA, res. Haverhill, MA, second marriage, divorced. Parents: Peter and Susan Clark (findagrave.com)

Complicating this is the fact that her second husband Frank Noyes' son Charles Everett Noyes, who died in 1877, name is on a stone in the Hillside Cemetery that seems to belong to the Cobb family, but Frank did not marry Mary until twenty-six years after Charles died.