Though Sanborn's teaching career started early, her side career as a published writer started even earlier: she was 11 years old when she published her first work (for pay!). Later, with help from fellow author Elizabeth Stuart Phelps, she began contributing to the Youth's Companion. As a short story writer, poet, and novelist, she mostly wrote for children. She also wrote a brief autobiography, which she called Memories and Anecdotes. Here is how she describes her own birth:
One summer morning, "long, long ago," a newspaper was sent by my grandmother... to a sister at Concord, New Hampshire, with this item of news pencilled on the margin:
"Born Thursday morning, July 11, 1839, 4.30 A.M., a fine little girl, seven pounds."
I was born in my father's library, and first opened my eyes upon a scenic wall-paper depicting the Bay of Naples; in fact I was born just under Vesuvius — which may account for my occasional eruptions of temper...
As years rolled on, I fear I was pert and audacious. I once touched at supper a blazing hot teapot, which almost blistered my fingers, and I screamed with surprise and pain. Father exclaimed, "Stop that noise, Caty." I replied, "Put your fingers on that teapot—and don't kitikize" [i.e. "catechize"]. And one evening about seven, my usual bedtime, I announced, "I'm going to sit up till eight tonight, and don't you 'spute." I know of many children who have the same habit of questions and sharp retorts. One of my pets, after plying her mother with about forty questions, wound up with, "Mother, how does the devil's darning needle sleep? Does he lie down on a twig or hang, or how?" "I don't know, dear." "Why, mother, it is surprising when you have lived so many years, that you know so little!"