The girl, identified by family members as Sasha Rodriguez, was one of two rave attendees who were in critical condition at California Hospital Medical Center after the 14th annual Electric Daisy Carnival.
As Sasha's family decided whether to remove her from life support Tuesday, her mother, Grace Rodriguez, told the CBS Evening News: "I was supposed to be planning her Sweet Sixteen party. Now I have to plan her funeral."
Sasha, who lived in the Atwater neighborhood, died shortly before 5:30 p.m. Tuesday, according Katreena Salgado, a spokeswoman for the hospital.
She and the other critically ill patient had been taken to the downtown Los Angeles hospital by ambulance directly from the venue, officials said. Both were treated for drug intoxication in the intensive care unit.
"She came in as an emergency patient from the rave. She was in respiratory arrest when she got here, and she never recovered," said Salgado, who said Sasha was in a coma and experienced multiple organ failure.
Outside California Hospital Tuesday night, friends and family said that when Sasha was found, she did not have identification.
"Obviously they didn't check IDs," said Eva Rodriguez, Sasha's godmother.
Doctors told Sasha's family that she had the drug ecstasy in her system when the ambulance got her to the emergency room.
Kimberly Keith, a family friend, said Sasha's loved ones are still trying to figure out what happened. Although they knew Sasha was going to her first rave, Keith said, drug use was "not her character."
When they got the call that Sasha had been taken to the hospital, they had no idea how serious her condition was.
"We were almost like joking, 'Oh she's going to be in trouble. I can't believe she went there!' " she said. Keith said they thought maybe the rave was "too packed, she was excited and passed out.... Never in a million years would we would have imagined" drugs.
A 16-year old friend who was with Sasha at the rave said Sasha was dancing, got hot and began quickly drinking cold water.
Doctors said "her sodium, electrolytes were so low that when she started replacing them so quickly [with cold water], ecstasy messes up your body's ability to process that, so it threw her body out of whack," said Keith.
Sasha passed out, hitting her head on the floor. The friend who was with her tried to shield her body but told her family that the venue was so crowded, people stepped on them.
"We've got kids in inappropriate situations that are dying," Keith said. "That's a city-, state-, county-owned building. They throw it, they rent it, yet they fill it full of minors in a setting where everybody knows what a rave is about. Where's the accountability?"
On Monday, Dr. Caitlin Reed, a physician from the U.S. Centers for Disease Control and Prevention on assignment with the Los Angeles County Department of Public Health, said she was at the rave on both days and did not see anyone checking identification.
"I didn't see any ID being checked at the entry point," Reed said. "This was an all-ages event. There were many, many younger teenagers present."
Pat Lynch, who manages the Coliseum, was stunned to learn of the death Tuesday.
"Oh, no. Oh, my God," Lynch said. "I don't know what to say. That's just terrible."
When asked how a 15-year-old was able to get into the event when the minimum age for entry was 16 without a legal guardian, Lynch said he needed to investigate.
"I'm at a loss," Lynch said. "Sixteen is what the promoter requested, and I just don't know."
Dr. Brian Johnston, the emergency room medical director at White Memorial Medical Center, called the death tragic. Johnston is among doctors who have said that raves at the publicly owned facility put people at risk. He believes that such parties should no longer be permitted at the Coliseum, which was built on state land and is under the authority of a joint city, county and state commission.
"I think it's tragic when a 15-year-old girl dies in this way as a result of a public policy that put her at risk," Johnston said. "Can you imagine explaining that to her parents?"
Barry Sanders, president of the Coliseum commission, issued a statement Tuesday expressing "dismay and deep sadness on the death of the young woman."
Sanders said he plans to call a special meeting of the commission to review all criteria required for organizers using the venue.
Pasquale Rotella, founder of Los Angeles-based Insomniac Events, the company that organized the event, did not respond to a request made through his publicist for comment.
The event, held Friday and Saturday, drew about 185,000 people to carnival rides, five stages and performances by Moby, Will.i.am, Steve Aoki and Deadmau5. About 120 required transport to local hospitals, mostly for drug intoxication.
The volume of patients in need of hospital care led several emergency room physicians on Monday to call for an end to raves at the Coliseum.
Cathy Chidester, director of the county Emergency Medical Systems agency, said Monday that officials treat raves at the Coliseum like a "multi-casualty incident," which she said was similar to planning for a disaster like the Chatsworth Metrolink train crash, which killed 25 and injured more than 130.
Tuesday's death was the latest in a string of high-profile problems at raves at public venues. Earlier this year, at least 18 drug overdoses tied to ecstasy were reported at a New Year's Eve rave at the Los Angeles Sports Arena, next to the Coliseum. And two men died of suspected drug overdoses during a Memorial Day weekend rave at the Cow Palace in Daly City, south of San Francisco.
Although many partygoers consider ecstasy to be safe, doctors and researchers warn that the drug, also known as MDMA, can cause high blood pressure leading to stroke. The hallucinogen can also trigger seizures, releasing toxins that cause kidney failure.
"There are multiple mechanisms through which ecstasy can cause death," Reed said earlier this month when a CDC report she co-wrote on the overdoses at the New Year's Eve rave was released.