But now decisive international collaboration is beginning to have an impact.
Rafaela is godmother to Milagros and has looked after her since her mother died as a child, treating her as she would a daughter.
When Milagros told her godmother about a job offer in a casino in El Salvador, Rafaela was immediately suspicious.
"I told her to be careful," she remembers, "but when she got a contract it all seemed OK.
"Her salary was going to be $1,000 a month - nearly 10 times her salary here in Nicaragua. And they said they would pay for her food and accommodation for the first two months too."
Leaving her baby with Rafaela in Managua, Milagros set off for El Salvador's capital, San Salvador.
As a teenage single parent, she dreamed of owning her own home. But in Nicaragua - one of the poorest countries in the region - this would be impossible.
Attracted by El Salvador's dollar economy, she thought she would be able to save money.
But Milagros had been duped. In San Salvador she was held prisoner in a brothel by men with guns.
Milagros called Rafaela secretly and told her she had been kidnapped. Rafaela heard the sound of gunshots before the line went dead.
For a moment, Rafaela thought she might have been killed, but then Milagros called again.
"I told her to try and remember any landmark - a mango tree or a large building - anything that might identify where she was being held," she remembers.
Milagros was beaten when she was discovered on the phone a second time. But then one of her guards took pity on her and let her call home a third time.
Armed with the information she needed, Rafaela phoned the police in Nicaragua who contacted El Salvador's trafficking unit:
"In a matter of seconds, the police in El Salvador went in and rescued her.
"When they got back to the police station, the sergeant called me. He was very happy and so was I. He said Milagros was in a terrible state, but - she was alive."
San Salvador is a noisy, busy city overlooked by a spectacular volcano. The streets are crowded with bars, in many sex is for sale.
I accompanied Sgt Jose Noe Ayala on a drive around the city to see the places where police have discovered trafficked women and children.
In one of the upmarket areas of the city, he pointed out a non-descript building, this was where Milagros was held.
"We rescued four girls that day," he tells me.
"Three were teenagers under the age of 18, all Salvadorians. And then there was Milagros, from Nicaragua."
After she was rescued, Milagros tried to commit suicide twice. Each time she first called Rafaela to ask for forgiveness and to say goodbye.
"She was feeling guilty. And responsible for everything that had happened to her," Rafaela says.
"I told her, there is no need to feel guilty. You have not done anything wrong."
There is a stigma attached to being trafficked because of the sexual nature of the crime.
This is the first time Rafaela has told Milagros's story. She wants the world to know what happened to her god-daughter.
"I am speaking out to you to say to any single mother or any adolescent, 'If you are offered a good job, do not be dazzled by the high salaries, because the price you pay is too heavy'," she says.
"We do not always have the courage to talk about trafficking, but we must be open about these things so this story is not repeated in other families."
After her rescue, Milagros was looked after in a new refuge for victims of trafficking in San Salvador. It is the only one of its kind in the region.
She received psychological support and also helped the police build their case against the group who trafficked her before being sent back to Nicaragua.
Rafaela will never forget the day Milagros returned.
"She was lovely, my little girl, but destroyed by her experience," she says.
Since returning, Milagros has stayed outside Managua, hidden somewhere the traffickers will not find her.
Now she is preparing to return to El Salvador to testify against her captors. Rafaela says Milagros is terrified.
"I know it is going to be very difficult for her," she says, "but I feel it is something that will help her get over what happened."
There have been few convictions for trafficking in Central America but Rafaela knows that this will only change if there is more cross-border co-operation between institutions, governments, and those who, like Milagros, became victims of the traffickers.