Eight years ago, Sarah Jackson went on an all-expenses paid trip with her church to learn about immigration at the US-Mexico border. At the time, she knew nothing about why people migrate, and viewed it as an opportunity to indulge her wanderlust with a free vacation.

“I was just living my perfect little life,” said the 34-year-old. “I didn’t know immigrant detention centres existed. I didn’t know about families being separated. I didn’t think there were people who were fleeing danger coming to the United States. It was not even a blip on my radar.”

The people she met on that trip – including a man fleeing Mexico after his pregnant fiancee was killed by a gang and a father with no criminal history who was deported from the US after police pulled him over for driving too slowly in a school zone – had such a profound impact on her that she pledged to dedicate her life to helping migrants.

“Over and over the Bible talks about treating the sojourner or immigrant as one of your own,” she told the Guardian, recalling the desperation of those she met at the border. “That’s not how we treat our own.”

Two years later, Casa de Paz (Spanish for “House of Peace”) was born. The Denver-based not-for-profit helps newly released detainees and their families get their feet back on the ground after months of immigration detention – offering a place to stay as well as food, clothing and transportation. It is also Jackson’s home, and guests are treated like family.

Most of us have a bad impression of America and are not expecting any good from anybody 32-year-old asylum seeker

Every evening, volunteers make the 15-minute drive to the Aurora Ice detention centre to collect those who have been released, either on bond or because they have won their immigration case, and bring them to the Casa.

The two-storey house looks exactly like every other in the tree-lined suburb. At the front door is a mat that reads “home”, with a heart in place of the “o”. Inside, it’s cosy and welcoming, with huge bowls of granola bars and fruit left out on the kitchen counter.

“Everything is ‘mi casa es su casa’,” Jackson said. “If you are hungry, eat. If you are thirsty, drink.”

When the Guardian visited in mid-September, one of the guests, a 32-year-old asylum seeker from central Africa, described his impressions of the Casa after spending seven months in Ice detention.

A welcome mat at Casa de Paz. Photograph: Chet Strange/The Guardian

“Most of us who have passed through the border and the detention centre have a bad impression of America and are not expecting any good from anybody,” he said, over a bowl of chilli con carne that had been brought round by volunteers.

“You are released into this strange place with no money in a country that has treated you poorly. Then you have this home where there’s free food, clothes, everything,” he added. “It is really amazing.”

Downstairs there are two guest bedrooms – one for men and one for women – with brightly coloured quilts on top of bunk beds. Upstairs there’s a room for families. On each of the 12 beds is a handwritten welcome note from a Casa volunteer, as well as a bag of travel-sized toiletries, a backpack and a towel.

Since guests are released from the detention centre wearing the outfit they were arrested in, the Casa also has closets filled with donated clothes for them to choose from, as well as shoelaces to replace those confiscated at the detention centre as a suicide hazard.

So far, more than 1,400 people from 23 different countries have stayed at the Casa, the vast majority asylum seekers from Central America. They can stay for up to three days although most leave sooner, eager to meet up with family or friends elsewhere in the United States.

Sarah Jackson looks at a map showing where different Casa de Paz residents have come from. Photograph: Chet Strange/The Guardian

Jackson, who has a day job selling software to churches, came up with an unusual funding model: volleyball. Each season, between 70 and 80 teams of six pay $250 each to participate in the “Volleyball Internacional” league that Jackson, a keen player herself, founded in Denver. All proceeds go towards the Casa’s rent and running expenses.

Zero tolerance, the subject of a major Guardian investigation this week, hit the Casa de Paz hard. Typically guests are happy to be released from detention, but over the summer they would arrive distraught and desperate to track down the children they’d been separated from within a system that wasn’t effectively keeping track of them.

I was just living my perfect little life. I didn’t know about families being separated Sarah Jackson

“It was extremely difficult to sit with people who were having a nervous breakdown over their missing children,” she added.

She recalls one Salvadoran mother who was trying to find her detained son by giving a physical description to a not-for-profit.

“She was saying, ‘He’s tall, he’s thin. He has dark hair and dark skin. He’s a quiet boy and he’s funny.’ That’s how they were trying to locate these children,” said Jackson.

During those months, the volunteers went into overdrive, raising money to bail parents out, connecting them with attorneys who could help track down their children and buying plane tickets to get them home.

Jackson found the lack of empathy for detainees among some members of her community troubling.

Fresh linens, a backpack, and toiletries await guests at Casa de Paz. Photograph: Chet Strange/The Guardian

“If your response to hearing that we were putting babies in jail – babies – is to question whether they are here legally, then it’s going to be hard to find any common ground,” she said. “The majority of these people are not criminals. They are coming here to ask for their human right to asylum. They weren’t breaking the law.”

That doesn’t stop anti-immigration trolls from targeting Jackson and the Casa online. She doesn’t have a sign on the outside of the house to avoid any harassment from passersby.

She tries to educate people where she can, inviting them for dinner to meet with the guests. Still, it’s an uphill battle – a member of her church recently told her that a “solution” to immigration would be for the government to put crocodiles in the rivers at the border.

For those not moved by her appeals to Christian values, Jackson also calls on American values.

“It’s important for citizens of this country to understand that our government has had a direct impact on the instability of these countries. In a sense we’ve created a lot of these conditions forcing people to flee,” she said.

Sarah Jackson reads a thank you note: ‘We read them to remember the impact our small acts of love can have.’ Photograph: Chet Strange/The Guardian

One silver lining to zero tolerance has been the surge in volunteers and donations, particularly as family separations hit the headlines. The Casa’s garage is stacked high with boxes of toiletries, clothes, cans of food, cellphones (which are topped up and given to guests) and bags.

On the evening the Guardian visited, at least 12 volunteers turned up at different points, some bringing food and groceries, others turning up to clean the bedrooms or assist the guests. When the Casa was filled to capacity over the summer, some of them even open up their homes to asylees.

Jackson is about third of the way through raising $400,000 to buy a bigger house next to the detention centre. Without rent to pay, the money from the volleyball league can go towards paying someone to staff the house all day, which will allow Casa de Paz to help more people.

Part of Jackson’s motivation comes from keeping and reading letters written by former guests, thanking her and the rest of the volunteers. “We read them to remember the impact our small acts of love can have on this world,” she said.

She translates part of one of the notes, handwritten on an A4 sheet of paper, surrounded by a border of hearts doodled in pink felt-tip pen. “I feel that God gave me Casa de Paz because he didn’t want me to get a bad impression of Americans.”