Depending on which book or newspaper article you read, Nellie Grant was either referred to as widowed or as divorced.
WidowedThe New York Times: "Mrs. Nellie Grant Sartoris, who has been sojourning at the Arlington Hotel, has finally decided to make Washington her permanent home. She has resided in England since the death of her husband..."
Source: "Mrs. Sartoris to Live in Washington", NYTimes.com, April 18, 1894.
The New York Times: "Rumor is constantly remarrying Mrs. Nellie Grant Sartoris ... Mrs. Sartoris, it seems to be accepted, is too attractive a woman to be left in widowhood."
Source: "Her Point of view", NYTimes.com, 12/30/1894.
The New York Times:
"Miss Vivien May Sartoris spent her early years in her mother's house, at 66 Cadogan Place, in the fashionable West End of London, where Mrs. Sartoris lived quietly with her three children after her husband's death."
Source: "Miss Sartoris Engaged", NYTimes.com, 8/15/1902.
Joint resolution of Congress readmitted Mrs. Sartoris to American citizenship: "Resolution May 18, 1898 (30 Stat. at L. 1496) Whereas, nellie Grant Sartoris, widow, daughter of the late General Ulysses S. Grant, being a natural-born citizen of the United States, married in eighteen hundred and seventy-four ... "
Source: Frederick Van Dyne, Citizenship of the United States, 1904.
Christopher Gordon: "All reports of Nelly's desire to seek a divorce "are entirely without foundation." The truth of the matter was that Algy had denied her a divorce. The whole sad affair came to an end in February 1893 when Algy, while living in a hotel on the isle of Capri, Italy, died of pneumonia at age forty-two."
Source: Christopher Gordon, "A White House Wedding: The Story of Nelly Grant", MoHistory.orgSummer 2005, page 19.
Sandra Quinn-Musgrove: "Four children were born to the couple, but shortly after the birth of their fourth, Sartoris died ... She petitioned the U.S. Congress for renewal of her citizenship. Congress complied. An American citizen once again, Nellie returned to the United States as a financially comfortable widow."
Source: Sandra L. Quinn-Musgrove, Sanford Kanter, America's Royalty: All the Presidents' Children, 1995, page 108.
DivorcedIshbel Ross: "... soon be on her way home, or would be suing for divorce. But when Marshall Jewell visited them in England some time afterward, he found her [Nellie] still infatuated with Algy."
Source: Ishbel Ross, The General’s Wife: The Life of Mrs. Ulysses S. Grant, 1959, page 239.
John and Claire Whitcomb: "Neither parent favored the marriage, even though Colonel Dent had opposed their own union. The groom's parents were dubious, knowing their son was troubled. The Grants tried to persuade Nellie that she was too young, but she had her way, as she always did. The White House wedding on May 21, 1874, was the subject of endless public fascination. Al elaborate bower of flowers -- some blooms were shipped from as far as Florida -- was constructed in the East Room. It stood on a dais covered with a rug, a gift from the sultan of Turkey. A huge wedding bell of flowers hung overhead ... Nellie, wearing a $2,000 gown, entered the room on the arm of her father, who the New York Herald noted, "looked steadfastly at the floor." He was later found sobbing in Nellie's room. Nellie and her new husband went home to England, and the marriage would eventually end in divorce."
Source: John Whitcomb, Claire Whitcomb, Real Life at the White House: 200 Years of Daily Life at America's Most Famous Residence, 2002, page 157.
William McFeely: "By the time she was thirty, Nellie Grant Sartoris was a miserably unhappy woman. Her English family closed down on her. She and her children were the property of a wretched husband. When she came to America at the time of her father's fatal illness in 1885, she wrote for permission for her children to join her so that she could remain with her mother for the year after her father's death. Permission was not granted, and she went back to the children in England. It was five years before she could wrench herself and her children away, return permanently to America, and get a divorce."
Source: William S. McFeely, Neil Giordano, Ulysses S. Grant: An Album, 2003, page 108.
Michael Korda: "Sartoris seems to have been a philanderer, a cheat, and a drunk ... but in case Nellie would eventually return to the United States with her children, though many years were to pass before she could get a divorce."
Source: Michael Korda Ulysses S. Grant: The Unlikely Hero, 2004, page 134.
Galena State Historical Sites: "She lived in England until her divorce in 1893 when she then moved back to the United States and lived with her mother, Julia Grant, until Mrs. Grant’s death on December 14, 1902."
Source: "Ellen “Nellie” Grant", GrantHome.com
Doug Wead: "By 1889, with Algernon’s drinking problem out of control, his esteemed family finally agreed that the daughter of the American president had suffered enough. Clearly, the famous storybook marriage that had charmed the public on both sides of the Atlantic was over. Nellie, who longed for a return to America, was not faulted. She was granted a divorce, provided a large annual income and finally allowed to take her children back to the United States, where a special act of Congress renewed her citizenship."
Source: Doug Wead, "The Greatest American Social Event of the Nineteenth Century", WhiteHouseWeddings.com
American Experience: "But after the couple moved back to England, Nellie discovered her husband was less dashing than he seemed. Some said Sartoris had problems with alcohol. Others said that he cheated on Nellie, or just plain ignored her. Nellie had four children by Sartoris. The oldest, a son, died in 1876. Nellie was never happy in her marriage. Eventually, she and Sartoris divorced."
Source: "Julia and Ulysses Grant's Children", PBS.org