LONG BEACH, California — The death of a 10-year-old Southern California schoolgirl after a fight with another female student was ruled a homicide Monday by the coroner's office.

Blunt force trauma to the head killed Joanna Ramos, who collapsed at home after a fight on Friday in Long Beach, coroner's Lt. Fred Corral says Monday.

He did not immediately have details about her injuries or the circumstances of her death.

The girl's older sister said Joanna died after surgery for a blood clot on the brain after the fight in an alley with an 11-year-old girl.

Joanna Ramos' mother rushed her to the hospital Friday evening after the girl began vomiting and complained of a headache, said Vanessa Urbina, 17, who was at the hospital with her sister.

Joanna was unconscious by the time she arrived at the emergency room, but hospital staff revived her three times before she went into surgery for the blood clot, Urbina told The Associated Press.

"They did surgery on her brain because she had a blood clot, and after surgery the doctor said she was still alive, and then a few minutes later he comes back and tells us that her heart stopped and they couldn't bring her back," Urbina said, crying as she sat on the steps of Willard Elementary School near a memorial of flowers and balloons.

In the hospital, "She was covered up, you could only see her face," Urbina said.

Joanna was pronounced dead at 9 p.m. local time Friday, about six hours after she and another 11-year-old girl had a planned fight near the school.

No arrests have been made.

The circumstances left family, friends and authorities seeking answers.

There were seven witnesses to the fight, which lasted less than a minute, police said. It didn't involve any weapons and no one was knocked to the ground.

Detectives have interviewed family and friends of both girls, but there is no indication that Joanna was bullied, police said.

"They took off their backpacks, and they put their hair in a bun, and then that's when they said 'go' and that's when they started hitting each other," Joanna's friend and classmate Maggie Martinez, who watched the fight, told KNBC.

Martinez and other friends said they tried to stop the fight, but were held back by boys who were watching and wanted it to continue.

Urbina, Joanna's sister, remembered her sibling as a happy child who liked to sing, dance and watch soap operas and loved having her hair curled by her older sister. She had asked Urbina to curl her hair for her birthday on March 12, and had asked her parents to take the whole family to an amusement park to celebrate.

"She was so young for this to happen" Urbina said. "She was so happy and so many people loved her."