A 16-year-old girl critically injured in a shooting at a Maryland high schoolthis week died on Thursday night after she was taken off life support.

The girl, Jaelynn Willey, was “surrounded by her family” when she died shortly before midnight, the St. Mary’s County Sheriff’s Office said. She had been at the University of Maryland Prince George’s Hospital Center since Tuesday, when another student shot her in the head in a hallway at their school in Great Mills, Md.

Earlier on Thursday, her parents said that she was brain dead.

“My daughter was hurt by a boy who shot her in the head and took everything from our lives,” her mother, Melissa Willey, said at a news conference at the hospital as she clutched her youngest child in her arms. 

Shortly before 8 a.m. on Tuesday, the police said, Austin Wyatt Rollins, 17, opened fire inside Great Mills High School with a handgun, striking Jaelynn and a 14-year-old boy. Jaelynn was shot in the head and collapsed in the hallway outside an art classroom, students said. The boy, Desmond Barnes, was shot in the thigh and was hospitalized. He has since been released.

The authorities were still trying to determine whether Jaelynn and her killer had had a relationship. The sheriff had said Wednesday that they did, but on Friday the office seemed to walk back that assertion, saying merely “they were acquainted.”

The shooting, which lasted about a minute, ended in a confrontation between the gunman and an armed school resource officer stationed at Great Mills High. The officer, Deputy Blaine Gaskill, responded almost immediately and fired his weapon at the gunman, who later died at a hospital. Deputy Gaskill was unharmed in the exchange.

While it was not immediately clear if the officer struck Mr. Rollins, the deputy’s quick response brought renewed attention to the national debate over gun control and how to prevent mass school shootings after the killing of 17 people at Marjory Stoneman Douglas High School last month in Parkland, Fla. Some politicians, including President Trump, have advocated arming teachers and placing additional police officers in schools. Others have criticized the idea.

Survivors of the Stoneman Douglas shooting have organized the March for Our Lives, a rally to end gun violence planned for Saturday.