She may have died of consumption (TB), just as her husband did a few years later.

She married Aaron Stephens of Washington Twp, Fayette Co, PA listed as Mary E. Stephens in the 1870 census living with her parents and having 2 sons, Levi (4) and Joseph W. (1). This is right after the Civil War and her husband is listed as having died of consumption in the Mortality Schedules for that year. She is listed with her father in 1880 as Lizzie Stephens (32) with her children Levi (12) and Joseph W. (10).
Was married a second time to Matthew Clark (according to Fran Kigan's book and Carolyn Dauner) and is listed age 62 with him in the 1910 census for her son Levi in Parma, ID. It says they were married 5 years and that both of her two sons were living at the time.
She died of chronic nephritis.
[Obituary] The Parma Review, Thursday 30 Nov 1916
Mrs. Mary E. Clark, mother of Levi Stephens of Apple Valley, passed away Tuesday afternoon at one o’clock after an extended illness. She was brought to Parma about two months ago from her home in Washington after her illness had summoned her son to the western state. At the time of her death, Mrs. Clark was 69 years old. The funeral was held Thursday morning at 10 o’clock, services being held in the Apple Valley Church by Rev. O. F. Merrill. Pall bearers were P. Rucker, J. Pettit, A. W. ____, A. Watts, Robt McIntyre and Robert Minton. Interment was at Parma cemetery. The sympathy of the community is with her family.