One reason Marisol Valles Garcia did not have much competition for the police chief job could be that her predecessor's head was left in front of the station a few days after he was kidnapped.

Another reason could be that a fifth of the population of Praxedis Guadalupe Guerrero, a dusty, sun-baked town on Mexico's border with Texas, has fled a wave of killings and burnings that have made this one of the most violent places on Earth.

It may also have been related to the fact that drug cartels tend to give police officers a choice of "plomo o plata", lead or silver, death or corruption – which is not much of a choice: if you take the plata, a rival cartel will likely fill you with plomo.

If being police chief of Praxedis for a monthly salary of not much more than £400 sounds like a career option from hell, you are not Marisol Valles Garcia, a 20-year-old criminology student who seized the offer and started her new job this week.

For an undergraduate who paints her nails pink and has an infant son to be thrown into the crucible of the drug war has astonished Mexico, but Valles Garcia appears to be sanguine: "I am frightened, I am only human, but you have to learn to trust and to have hope that things can change," she said. "Have faith that we can do something about this security problem. We want to build a place where young people can fulfil their hopes and dreams."

Valles Garcia has yet to make an arrest but has become an instant celebrity and been hailed Mexico's bravest woman. She brushed off the praise. "I don't think age is important," she said. "What is important is what is going on inside. What I feel and what I believe. We were not looking for publicity. I don't know how the information got out."

She heads a force of just 13 agents, nine of them women, with one working patrol car, three automatic rifles and a pistol. The town is small – just 8,000 people after the recent exodus – but it sits in Juárez valley, a strategic route once used by Apaches and Billy the Kid and now a transit point for cartels transporting cocaine, cannabis and other drugs to the US, which is a stone's throw across the Rio Bravo.

The previous police chief, Martin Castro, was abducted in January 2009 and his severed head turned up days later in front of the station, a warning that frightened away most of the force and left the police chief post unfilled for over a year.

The Sinaloa cartel is said to be waging an extermination campaign against the homegrown Juárez cartel in the valley, making it one of the deadliest fronts in a war that has claimed 28,000 lives in the past four years. Earlier this month a new mayor, José-Luis Guerrero, started interviewing candidates for a new community police force. Valles Garcia, a student from Juárez university who is due to finish a criminology degree in December, was working as the police secretary and applied to be a regular police officer. She so impressed the mayor that he offered the top job.

"To those who say we are naive and she doesn't have the experience, we say that the traditional methods have not worked," said Andres Morales, the mayor's chief of staff. "We know that the results will not be immediate. We are thinking of the medium and long term. Of laying the foundations for something better in the future."

Valles Garcia's force will focus on community policing and, in theory, leave the gunbattles to the army and national police. "We are only going to do crime prevention work," she said. "We do not have the means to take them [organised crime] on. Taking on the other stuff is the job of the state and federal authorities." She implied that she would not even report the presence of organised crime in the town.

Appointing a student was not a gimmick, said Morales: "We never imagined the kind of attention it would get, but we are not complaining. It helps us send a positive message to the community."

Valles Garcia has refused bodyguards because they would distance her from the community, imply she was frightened and not do much to protect her anyway.

Leading commentator Héctor Aguilar Camín welcomed the appointment. "People may be frightened and besieged, but they have not surrendered," he said.

Farmer Arturo Gomez said he would give the new chief a chance. "This is a town without law," he said. "It is not likely things will change from one day to the next, but let's see what a woman can do... things can't get any worse."

Fidel Vega, a petrol station employee, added: "Here, everybody is afraid, and anything that can be done to remove that fear would be good. This girl has a desire to get things done."

However, some traditionalists are upset. "Are there are no men in the state of Chihuahua?" asked one blogger.

Killing zone

Mexico's drug war exploded in 2006 after President Felipe Calderón launched a military-led crackdown on the cartels which smuggled billions of dollars worth of cocaine, cannabis and other narcotics to the US. The cartels fought back against the state – and each other – with a savagery that has since claimed 28,000 lives. The violence, including car bombs and beheadings, has turned parts of border states such as Tijuana and Chihuahua (which includes Juárez valley) into lawless killing zones. Cartels infiltrated poorly paid municipal and state police until entire forces were disbanded and reformed from scratch, only for corruption to re-emerge. The federal police, once considered relatively honest, have been tarred by complicity with drug lords. Rory Carroll