Before she died, her mother, Melisa Willey, told reporters that the 16-year-old had "no life left in her," according to The Baltimore Sun.
"My daughter was hurt by a boy who shot her in the head and took everything from our lives," Melissa said. "It will be different forever."
Willey was left brain dead after a 17-year-old boy shot her in the head. She died at about 11:30 p.m. Thursday, the St. Mary's County Sheriff's Office said.
"It is with heavy hearts and great sadness we provide this update," the sheriff's office said in a statement.
Melissa Willey spoke to reporters Thursday evening at the University of Maryland Prince George's Hospital Center, where Jaelynn was being treated. Melissa held Jaelynn's youngest sibling as she shared the news with her husband, Daniel, by her side.
Other family stood behind Melissa as she spoke and a group of friends stood off to one side.
Jaelynn was rushed to the hospital after the Tuesday morning school shooting at Great Mills High School.
Authorities have said that 17-year-old Austin Wyatt Rollins, also a student at the St. Mary's County high school, used a handgun to shoot Jaelynn. A 14-year-old boy, Desmond Barnes, was also shot in the leg.
Rollins exchanged gunfire with the school resource officer, County Sheriff's Deputy Blaine Gaskill. Rollins later died at a hospital.
Barnes was released from a hospital Wednesday after being treated.
Before Jaelynn was identified to the media, St. Mary's County Sheriff Tim Cameron told reporters that investigators believe Rollins had previously been in a relationship with her. Cameron also specified that it's unclear whether it was Gaskill's bullet that took Rollins' life, though he did praise the deputy's response time.
"He responded exactly as we train our personnel to respond," the sheriff said. "This is what we train for, this is what we prepare for, and this is what we pray that we never have to do. On this day, we realized our worst nightmare."
"The notion of 'it can't happen here' is no longer a notion," Cameron reportedly added.
Within minutes of the Great Mills shooting, survivors of the Parkland, Florida school shooting took to Twitter to share their condolences with the victims.
The news of the Maryland shooting broke quickly, as the nation continues processing the epidemic of mass shootings and gun violence plaguing schools and other public venues. Last month, after the tragic attack on Marjory Stoneman Douglas High School, which took 17 lives, many student survivors took up the cause to prevent it from happening again. They coined the hashtag "Never Again," and channeled their grief into activism, organizing marches and school walkouts.
On Tuesday morning, the most outspoken among the Parkland student activists tweeted their support for the students of Great Mills.
"We are Here for you, students of Great Mills together we can stop this from ever happening again," tweeted Emma Gonzalez.0comments
"Less than a WEEK ago Great Mills High School students walked out with us to protest gun violence...now they're experiencing it for themselves," wrote Jaclyn Corin. "The state of our country is disgusting - I'm so sorry, Great Mills."
The teenagers have not let up in nearly five weeks since the devastating attack in their own hometown. On Saturday, they will lead a march in Washington D.C. along with like-minded activists from around the country. The event, called March For Our Lives, has received wide coverage in recent weeks. It has gotten huge donations from celebrities, including George and Amal Clooney and Oprah Winfrey. Others, including Justin Bieber, Amy Schumer and Julianne Moore, have expressed their support for the cause.