ROSEDALE, Queens (PIX11) — A teenage girl killed in Queens was a college freshman who died the day before her 18th birthday, her mom told PIX11 Tuesday.

Shantasia O’Brian, 17, was found unconscious and unresponsive with a gunshot wound to the back on Friday. Police arrested a 15-year-old boy on manslaughter charges in connection with her death.

“She didn’t deserve this,” Karen O’Brian, the teen’s mom said through tears. “And I can’t, I just don’t understand at all.”

The suspect was apparently the younger brother of O’Brian’s boyfriend, sources said. He was playing with the gun and the shooting may have been accidental.

O’Brian was sitting in a car with her boyfriend and the alleged shooter when she was killed. The teen was home for the holiday weekend. She’d moved into the dorms for the College of Staten Island just weeks before her death. The teen asked her mom if she could go hang out with friends.

“I told her she could have went and then she never made it back home,” the teen’s mom said.

The heartbroken mom hasn’t slept in the days since her daughter’s death, she said. She’s planning a funeral and wondering why a 15-year-old boy allegedly had a gun in the first place.

“Where would you get a gun at 15? Why would you have a gun? Why would you need a gun? Why would you need a gun? What were you doing? And now my baby’s gone,” she said.