In 1847, she removed to Warrensburg, New York before moving to Miller's Tavern, Virginia to serve as principal at the Midway Female Academy.

[4] Writing to a friend soon after her arrival in early 1851, Fay said:— "It is a difficult thing to keep the heart at the spiritual heights it has gained, and perhaps the first rude shock to the young missionary's faith, on his arrival in heathen lands, is the utter indifference of the people, the clouds of incense that dim his sight, and the harsh music that deafens his ears, as he finds himself in some lofty temple, near huge idols, before whom crowds are prostrating themselves and offering all the worship their darkened, untaught hearts are capable of, and I exclaim, 'Who is sufficient for these things, and how can the still, small voice of the Spirit ever touch the hearts of these noisy idolaters, or how can the missionary be seen through the clouds of incense, or the voice be heard in the din of gongs and drums?

In 1860, Fay moved with her students to the Church Missionary Society, in which she had been obliged for a while to work in consequence of a lack of means to sustain the school.

[5] She established in her own house in Shanghai a boarding school for boys, which she called her "gravest responsibility," as through this agency she hoped to raise up teachers and preachers who would carry on future work.

She not only taught in the school, carried all the domestic cares, provided for the clothing, kept all the finances, but devoted much time to the study and translation of the Chinese language.

[7] A few years later, a donation from some women in Pittsburgh, Pennsylvania, together with a little money contributed in Shanghai, enabled Fay to receive a few more boys, so that the school numbered twenty pupils.

In addition, she traveled to Kong Wan with Mr. Nelson on Sundays and Thursdays, where she has charge of a girls' school, and attended the sick in the hospital.

Her later life included several age-related illnesses so that, from the mid-1860s, she took extended breaks from her work, either resting in her room or at Chinese sanatorium towns.

The funeral was attended by a large number of visitors and residents, and the flag of the United States Consulate was put at half-mast in token of respect to Fay.