The 15-year-old girl, Aiesha Baker, was brutally punched and kicked in the head Jan. 28 at the tunnel's Westlake Station and robbed by four people who stole her purse, phone and iPod before fleeing the scene.
Security cameras captured the attack on video and show three guards standing around, taking no action to intervene or stop the assault.
And the girl, who appeared with her mother and an attorney at a news conference Friday, said she tried to convince two uniformed Seattle police officers to help her before the attack, but they just told her to "clear the area."
She said the same officers showed little interest in investigating or helping her after the attack, either, and the tunnel guards didn't even call anyone on their walkie-talkies.
"I'm angry at what they did to me - and the police could have prevented it, the security guards could have prevented it, it could have been a situation that didn't have to happen," Aiesha said.
The girl's mother, Letta, who rushed downtown to help her daughter after the attack, called the whole incident an "outrage."
She said her daughter has a potentially fatal heart condition and could easily have died in the attack. "Then we would be looking at murder charges," she said.
When asked her reaction to the videotape of her daughter's beating, she said, "I just can't explain how I felt" before breaking down in tears.
She said she had to threaten to call a Seattle city council member before police officers showed much interest in helping her daughter or looking for her attackers.
An attorney for the victim's family, James Bible, claimed at the news conference that police and the security guards would have reacted differently if the victim had not been black.
"If this young lady had had blond hair and blue eyes and told police, 'These black kids are following me,' the response would have been different," he added.
"What would have happened if there wasn't a video? Would we be here now?" he said. "Young African-American children need to be able to reach out to law enforcement.
"This would not have occurred if officers had taken the time to investigate an incident when she said, 'These people are threatening to harm me - the response can't be to 'just leave and get out of our faces.'"
He said there is a "substantial likelihood" that a lawsuit will be filed over the incident.
In the aftermath of the attack on the girl, King County Executive Dow Constantine said Thursday uniformed, armed deputies are being deployed in the downtown transit tunnel as an interim step during a review of the contract with the firm that employs Metro guards.
"These new measures will assure transit customers of a police presence that meets their expectations for safety and security in the bus tunnel," Constantine said.
Baker was knocked unconscious during the Jan. 28 attack but has since recovered.
A 15-year-old girl who is accused of being the primary attacker pleaded not guilty in juvenile court Thursday to assaulting and robbing Baker. She faces up to 2 1/2 years in juvenile detention if convicted.
Three other suspects also are charged with first-degree robbery. Those three will be charged as adults in King County Superior Court.
Baker told a King County sheriff's detective that the group followed her from a nearby department store into the bus tunnel after police officers told her to leave the store.
She said officers refused to accompany her to the tunnel even when she explained she was being followed and stalked by a large group of people.
Once inside the tunnel, she said she deliberately stood next to the three guards for protection.
"I went to the security and told them that these kids were trying to jump me," Baker said. "I know that I am about to get jumped and I am hanging around the guards to try and get protection. ... I thought the security guards would defend me."
The guards didn't intervene, though, as the attack on the girl escalated.