(CNN) -- Authorities are investigating whether it was an extreme case of bullying that led to the death of a 17-year-old student in Argentina, after she was attacked by two women and another girl last week.
Naira Cofreces died Sunday of multiple injuries, including bruising to the left side of her brain, officials said.
"First there was a verbal altercation and then she was kicked, punched and Naira's head was smashed against a wall," Judge Maria Laura Durante told Telam, the Argentine state news agency. The judge also said this is a case of "aggravated homicide because there might've been premeditation."
Officials say the teen was attacked last Wednesday at about 10 p.m., after leaving the night school she attended in the city of Junín, about 260 kilometers (161 miles) west of Buenos Aires. Her attackers, ages 17, 22 and 29, were waiting for her after school. The two younger ones were her classmates. All three have been arrested and charged with aggravated homicide, authorities said.
"There's no clear motive. We have testimony that suggests the motive could've been another girl or because they (the victim and her friends) acted as if they were more beautiful than the rest and dressed better than them," Durante told Telam.
A close friend of Cofreces told CNN affiliate Channel 9 the dispute started over differences that the victim and her alleged attackers had over looks and demeanor.
"She (one of the attackers) would tell her that she had a snobby face, an old woman's face, that she thought she was more beautiful than her and that she walked as if she were a model. That's how the whole problem started," said the friend, who was not identified because she's a minor.
Cofreces went home after the attack, but was taken to Agudos General Hospital the following morning. "She came the day after she was beaten up, we did a tomography and discovered a big hematoma on the left side of her brain, so we decided to operate," Dr. Carlos Garbe told Telam.
A new tomography revealed more bruising of the brain. leading to a second surgery. "After the second surgery, she continued to show complications which worsened until she died," Garbe said.
Cofreces was pronounced dead Sunday night, four days after the attack.
The incident has caused a public outcry in Argentina. Nestor Ribet, education undersecretary for the Buenos Aires Province, says he has sent counselors to Junín to work with students and their families at the school where the attack took place.
"We're talking about the death of a 17-year-old child. Nobody can explain why this happened," Ribet told Telam. "There is really nothing that can explain this."