She served as the head of Fiske Seminary, a girls' boarding school in Urmia, West Azerbaijan Province.

[2][1] Mount Holyoke Seminary graduate Fidelia Fiske founded Fiske Seminary, a girls' boarding school at Urmia in 1843, to educate Christian Assyrian girls (which at the time were referred to as "Nestorians", and is no longer a preferred term)[3] and to train teachers.

[6][7] In 1890, the Urmia mission reported that "Miss Dean, the faithful worker of twenty-two years, has been quite broken down... she has never given up entirely, and her presence, her experience and her spirituality exert untold influence over the girls of the boarding school.

"[8] Nancy Jane Dean left the mission field in 1892, in poor health.

[15] In retirement, Dean continued to lecture on Persia and work with Presbyterian women's groups.