Previous researchers had believed her to be the daughter of Charles Henry Joy (Joy-1338) and his wife, Marie Louise (Mudge) Joy (Mudge-484). This is likely wrong as the birth records indicate she was born in Quincy, while that family (see above) lived in Boston, and her father, a Charles H. Joy, was a milkman also born in Quincy, MA, which Charles Henry Joy was not. Moreover Mary Agnes' mother was listed as "Margaret," born in England. Again, clearly not Marie Louise Mudge.
Corroborating this, another researcher writes, "she is not listed in 'Thomas Joy and his descendants.' She's not mentioned as being at Ellen's wedding (Table Gossip, Boston Globe, Nov. 6, 1904, p. 42). Similarly, she wasn't listed on the Joy trip to Liverpool on the Pavonia as reported in the Globe on Nov 16, 1887 (Edith, Ellen, and Ben all went)."
Future researchers should probably avoid linking this person with that family.
Have you taken a DNA test? If so, login to add it. If not, see our friends at Ancestry DNA.