CHICAGO — The mother of a transgender student said her daughter had suffered greatly since being banned from the girls’ locker room at a suburban Chicago high school.

The comments, published on the website of the American Civil Liberties Union of Illinois, were the first by the family since the federal Department of Education found this month that Township High School District 211 in Palatine had violated the girl’s rights under Title IX, a federal law that bans sex discrimination. The A.C.L.U. is representing the girl in a federal complaint against the district.

The student’s name has not been released, and the mother’s name was not published with her roughly 1,000-word essay, titled “Our Child Is a Girl.”

The mother described the family’s struggle with the daughter’s identity and the effect of not being able to use the girls’ bathroom or locker room or play on a girls’ sports team. She said her daughter had been “bullied on a daily basis.”