Eunice met her husband Seth when he was taking his medical training with her father, Dr. Bezeleel Mann. In 1832 she is listed as living in Montgomery, NY. On 21 Jan 1839, she is listed on Revolutionary War pension abstracts, as being a resident of Orange County, NY "to be near her children". She later traveled with her daughter, Louisa, and son-in-law, David Thiers, to McHenry County, Illinois, where she died at an advanced age.

Louisa wrote of her mother, "[She] ordered well her household, being a woman of strong intellect, and she commanded through a long life the respect and love of all who knew her." She also related an anecdote which expresses to some degree Eunice's independence of mind:

"[My] parents had brought with them the New England customs and in a measure the religious beliefs prevalent at the time. If the doctor was held in great respect in old New England, what shall we say of the minister? In no other section of the country had religion so firm a hold upon the affections of the people. He was to them a just man made perfect, a sure guide to truth. Under such influences [my] mother hardly dare question his teachings, but she did draw the line when he proclaimed from the pulpit that "Hell was paved with infants not a span long."

This minister supported predestination, the belief that people were destined for heaven or hell from the moment of birth, and that nothing could be done to influence God's will in the matter. Perhaps Eunice was thinking of her brothers and sisters who died in infancy, or her own baby daughter Bebe, who died one sad Christmas, when she made her protest against the idea that babies not old enough to sin could go to hell.

Eunice and her husband Seth were third cousins once removed. Both were descendants of the early Massachusetts pioneer Jonathan Fairbanks and his wife Grace.