She began writing in the 1840s, publishing poetry and children's stories. She later became an assistant editor of the highly-successful Godey's Lady's Book under Sarah Josepha Hale, before founding her own children's magazine with her husband in 1853. Though she often wrote on behalf of women's rights and abolitionism, Greenwood is mostly remembered for her highly sentimental fiction works aimed at girls.
One of her stories, "Bessie Raeburn's Christmas Adventure," follows a familiar pattern for early sentimental writing. The great revelation of the story comes on the birthday of one of the main characters, a young girl named Lily. She asks a servant-girl turned friend-of-the-family the date of her birthday. The girl, Mary, says she doesn't know because she never knew her parents or her origins. "I do not know exactly how old I am," she says, "but I think about fifteen."
"About fifteen!" repeated Mrs. Phillips, in a dreamy way, "and your name [is] Mary. John, our Mary would have been just about her age, could we have kept her; and do you know I fancy she would have looked very much like this young girl... I have an odd idea that she looks like our family, somewhat as I used to look; and, stranger still, like you, John... O John, John, tell me! Can she be! O blessed God! —"
She could not utter a word more, but she stretched out her trembling arms, and Mary crept into them and lay on her mother's breast, the long hunger of her heart satisfied at last!
"Yes, dear, this is our lost child, given back to us by a gracious God," said Mr. Phillips. But there was no need to tell her that; she knew all now. Kissing her darling, patting her head, and murmuring over her sweet pet names, as though Mary were still the baby girl she had lost.