WASHINGTON — The Justice Department has deported an Afghan woman who became the first person brought before the Alien Terrorist Removal Court, ending the case before a broader legal challenge could determine whether the little-used tribunal is constitutional. Nazira Haji Zada agreed to be designated an “alien terrorist,” gave up her status as a lawful permanent resident and accepted deportation, according to court filings unsealed Sept. 11. Prosecutors agreed that her admission could not be used against her in a future criminal case. The department said Haji Zada had pledged allegiance to the Islamic State and helped two relatives in an alleged plan to carry out an ISIS-inspired mass shooting in the United States on Election Day in 2024. Her son, Abdullah Haji Zada, and son-in-law, Nasir Ahmad Tawhedi, were previously arrested and convicted, the department said. “​​As the matriarch in her family, she supported a plot to commit an ISIS-inspired mass shooting on Election Day in 2024,” the Justice Department said in a statement. Haji Zada was brought before the court in July and left the country roughly two weeks before the department announced the deportation on the 25th anniversary of the Sept. 11 terrorist attacks. U.S. District Judge Joan Ericksen approved the agreement. Congress created the Alien Terrorist Removal Court in 1996, but it remained dormant for nearly three decades. The Trump administration revived it as part of its effort to remove noncitizens accused of terrorism, but the court’s secretive procedures immediately raised due-process concerns. Haji Zada’s lawyers had planned to challenge the court’s handling of classified evidence and other procedures. At the court’s first public hearing in July, Ericksen indicated she might grant at least some defense requests for access to information. Those questions will now remain unanswered. The deportation agreement eliminates the immediate legal dispute over whether the tribunal’s procedures satisfy constitutional guarantees of due process, while leaving the government with a specialized removal mechanism that has received little judicial scrutiny. The court has five judges selected from across the country by Chief Justice John Roberts. Its structure resembles the Foreign Intelligence Surveillance Court, which reviews government applications to monitor suspected agents of foreign powers. An attorney for Haji Zada did not immediately respond to a request for comment.