In the United States, until the passage of the 1922 Cable Act, a woman lost her United States citizenship upon marriage to an unnaturalized alien. That’s why this native of New York State is listed as an alien in the 1920 census–with no date of arrival in the United States.
“Any woman who is now or may hereafter be married . . .” by Marian L. Smith on the National Archives website provides more detailed information.