Who is Mary Smith-Ellis Thomas from Stern Men and what is their importance?

Protagonist Ruth Thomas' mother, Mary inherits the onerous job of serving as lady-in-waiting to the spoiled and demanding Vera Ellis of Concord, NH, when her mother drowns while knitting beside the sea. Mary is allowed just enough education not to be a dull companion and then takes over her mother's odious chores. This keeps Mary too busy to have friends or lovers, but in 1955, Vera wants to throw a community picnic on Fort Niles Island and the work falls to Mary. She is assisted by Stan Thomas, who is soon smitten with her.