If they fail to comply, the judge said, Sessions, Homeland Security Secretary Kirstjen Nielsen and other senior Homeland Security officials would have to convince him not to hold them in contempt of court.
U.S. District Judge Emmet Sullivan said the government appeared to have "spirited away" the woman and her child.
Activists rally against the Trump administration's immigration policies outside the New York City offices of U.S. Immigration and Customs Enforcement in July.
The plaintiffs on the plane are identified in the lawsuit as Carmen and her minor daughter, although Carmen is a pseudonym, the network reported.
"Upon arrival in El Salvador, the plaintiffs did not disembark and are now en route back to the United States", the department said in an emailed statement.
In court on Thursday, Sullivan also temporarily blocked the USA from deporting plaintiffs in the lawsuit, most of whom are women fleeing sexual abuse and gang violence.
American Civil Liberties Union attorneys and the Justice Department agreed to delay removal proceedings for the mother - named only "Carmen" on documents - and her child until 11:59 p.m. Thursday so the matter could be argued in court, the Post said.
According to the Post, attorneys for Carmen learned "during a brief recess" in court that the woman and her daughter had been removed from a family detention center and were heading for an airport in San Antonio.
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After that, it was easy pickings for Njoku, who ran past Ogletree for an uncontested 36-yard touchdown pass from Tyrod Taylor . In three years at Penn State, Saquon Barkley racked up 1,195 rushing yards and eight touchdowns on 5.7 yards per carry.
"Carmen and her daughter are right now somewhere in the air between Texas and El Salvador", ACLU lead attorney in the case Jennifer Chang Newell told NBC. Several coworkers at the factory where Carmen worked had been murdered, and her husband is also abusive, the records state.
Carmen and her daughter were not separated when they crossed the border, but their chances of remaining in the USA were slim after she failed a "credible fear" test created to determine whether her asylum claim could be honored.
In June, the Trump administration determined that fleeing domestic violence and gang violence would no longer be accepted as a means for refuge in the United States.
The ACLU is asking the court to invalidate a decision by Sessions that says most victims of domestic abuse and gang violence can not qualify for asylum. In the suit, Grace said her partner of 22 years, and his two gang member sons from another relationship, repeatedly beat and threatened to kill her and her children.
Sessions and other Trump appointees have dramatically shifted how the federal government speaks about asylum, going as far as to suggest in public communications the unproven claim that asylum is a routinely abused legal loophole.
Sessions has led efforts by the Trump Administration to crack down on illegal immigration, including the adoption of a zero tolerance policy that briefly included separating immigrant parents from their children while they were in US detention.
Asylum seekers previously had to show that the government in their native country was "unable or unwilling" to protect them.