Editor's note: Tune in to AC360° Monday at 10 p.m. ET to see Ed Lavandera's report about Marisol Valles Garcia.
El Paso, Texas (CNN) -- When the cell phone rang, the words "private number" flashed on the screen. Marisol Valles Garcia knew who was calling. The threatening, mysterious voice on the other end of the line had hounded her for almost four months.
But this phone call had a starkly sinister tone. The man said something he'd never said before. He was coming to pick up the 21-year-old police chief at the station. "Some people" wanted to see her, he said.
The same day -- March 1 -- her mother spotted strange cars driving past the family's home. Valles Garcia knew it was only a matter of time before they closed in.
She called her husband and told him to grab their 1-year-old son. Four months after headlines around the world heralded her as the "bravest woman in Mexico," Valles Garcia plotted a hasty escape across a remote border crossing in West Texas.
Terrified of being tortured or killed, she fled the country without packing a suitcase.
With her parents, sisters, husband and son, Valles Garcia crossed a footbridge into the United States and asked for asylum.
"I came here for the security my country cannot provide for me," she told CNN in a recent interview. "The fear will never go away. What I experienced is a fear that will last a lifetime."
A few days after she left Mexico, Valles Garcia learned her mother's house had been ransacked. She is hiding in the United States while she awaits a ruling in her asylum case, and agreed to speak with CNN in El Paso, Texas.
The asylum process is a lengthy legal road that could take up to three years, El Paso attorney Carlos Spector said, and there's no guarantee U.S. authorities will grant the request.
But Spector said one thing is certain: Going back to Mexico would be a death sentence.
"I have no doubt she will be killed," said Spector, who calls Valles Garcia "the Rosa Parks of Mexico."
"She is a trophy for the cartels. She represented the average person saying, 'No more,'" he said.
Last October, Valles Garcia took a job no one wanted. She became police chief in the small Mexican border town of Praxedis G. Guerrero.
The previous police chief had been murdered. Drug cartel assassins cut off his head.
Nationwide, the Mexican government says there have been more than 34,600 drug-related deaths since President Felipe Calderon began a crackdown on cartels in December 2006.
Praxedis, located only about 35 miles away from Ciudad Juarez, is in a region that has seen some of the bloodiest conflict, as rival cartels fight over smuggling routes into the United States.
The idealistic criminology student's rise to police chief in one of Mexico's most violent areas thrust Valles Garcia into the international spotlight. News reporters from around the world came to Praxedis, a town of only 3,000 people, to tell the story of the woman who dreamed to make a difference.
"We had a beautiful idea. That's why I accepted the job," Valles Garcia said. "We wanted to re-establish people's confidence in the police."
But just weeks into her new job, the threatening phone calls started, Valles Garcia said.
At first, the man on the phone tried to convince her to work for both sides.
To many public officials in Mexico, it is a familiar offer, commonly referred to as "plata o plomo" (silver or lead) -- a not-so-subtle demand to accept the drug cartel's bribes, or be on the receiving end of bullets.
Valles Garcia refused the offers for months. Knowing she could not take on the drug cartels with her tiny police force, her mission at the police department was focusing on prevention.
She hired 13 female police officers. They refused to carry weapons and the young police chief never used body guards, unlike many other public officials in Mexico.
"Yes, there is fear," Valles Garcia told CNN shortly after she started the job. "It's like all human beings. There will always be fear, but what we want to achieve in our municipality is tranquility and security."
Her vision was training the police force to focus on pushing children to stay in school and helping single mothers find steady-paying jobs.
It was a lucrative offer in a town full of women widowed by the drug war, where many families were scrambling to survive. Valles Garcia hoped the same circumstances that made so many young people fall prey to drug cartels' offers of making easy money would bolster her police force's success.
"We were helping the people they (the cartels) were recruiting from," Valles Garcia said. "I don't think they liked that. We were trying to help them make a better life."
But perhaps naively, Valles Garcia said, she didn't expect to be run out of her hometown by the narco underworld.
"I thought we made it clear to the drug cartels, we were going to be focused on social issues," said Valles Garcia. "We weren't going to attack them. That was the job of the state and federal police."
But the threats kept coming.
Eventually, Valles Garcia became so frightened that she asked her father to drive her to work.
Now, she fights back tears as she acknowledges that she can never return to the only place she's ever lived -- a violent, corrupt world where many of her friends and family remain.
"My whole life was in Mexico," Valles Garcia said. "I hope Mexico becomes what it once was, a safe, fun place with life."
Valles Garcia is devastated that she can't go home, and disappointed she couldn't finish her three-year term as police chief of the small town where she was born and raised. But still, she's proud of her accomplishments.
"We at least made a difference, gave people a little hope," she said.