Isabella Acevedo gazes out at the farmyard-themed play area outside the visiting room at the Yarl's Wood Immigration Removal Centre and considers the ugly symmetry of the previous week's events.

Last week the Conservative MP whose central London flat she once cleaned, Mark Harper, was reappointed to the government as a junior minister at the department for work and pensions, just five months after his discovery that Acevedo had been working for him illegally prompted his resignation as immigration minister.

Three days later, Acevedo was summoned from a Haringey town hall ceremony room minutes before her 19-year-old daughter was due to be married there, marched to a waiting van by around seven immigration enforcement officers and taken to Yarl's Wood. Unless an 11th-hour legal challenge is successful, she will be deported to Colombia on Thursday.

"I saw Mr Harper on TV," Acevedo, 47, says. "He is still with his rich friends, still earning good money. Me, I have lost everything: my job is gone, my friends are gone, my dignity is gone. In one day my whole life has changed."

She chews at her bottom lip. "I'm scared. I don't know what will happen to me in Colombia." Later, she radiates pride as she enthuses about her daughter's artistic talent and success at school, then cries at the memory of being torn from her only child on her wedding day, to be sent 5,000 miles away.

"For weeks I had been saving up, £5, £10, to buy the shoes, the flowers, the cake. My daughter has had such a hard experience and now on the most important day, the day of this one good thing, this happened. I didn't even get to see her in her dress."

Earlier in the day we spoke at length on the phone, Acevedo explaining how she brought her daughter here in 2000 when she was five, seeking a brighter future for her than the violence and poverty offered by her home country. Acevedo had studied fashion and comes, in her own words, from a humble, hardworking background. But there had been no jobs in the city where she grew up, and seeing her husband's father kidnapped for a ransom provided another spur to leave; she left her husband behind, but with a plan for him to join them later.

With little English and no papers allowing her to work, she failed to find a job in fashion in London, and eventually started cleaning offices, sharing a single bed with her daughter in a room where two other immigrants also slept, and juggling shifts with school runs.

Within a few years, she had begun cleaning flats in a luxury complex in Waterloo, and in 2007 started working for Harper, after being sent there by a member of security staff. Once a week she was paid £30 in cash to clean and iron for three and a half hours. She got no sick pay or holiday pay. At Christmas, the Harpers gave her a £30 bonus. Her pay never increased in seven years. "I never had the guts to ask for more," she says. "You know what it's like, the life of an immigrant: you just take what you're given, you want to live a simple life."

'They told my friend to tell me that the person I was working for was very important and I couldn't be here any more'

She only met Harper twice in the seven years she worked for him, finding him to be "very polite" on both occasions, but had a more personal relationship with "Mrs Margaret", his wife. "I wouldn't consider her a friend," Acevedo says. "But being around for seven years ... we talked about things, like when my daughter's work was in an exhibition. She was sweet to me."

Yet until February she had no inkling of who her employer was – not even that he was an MP, let alone the minister for immigration. "I only found out when the problems started," she says. One Saturday morning, at 5.30am, immigration officials turned up at the house where they thought Acevedo was living. Finding no one there, they knocked down the door, then padlocked it when they left.

"Then the calls started," she remembers. "They left messages simply saying: 'We want to talk to you'. All that morning my phone was ringing." Later, a friend with better English took one of the calls. "They told my friend to tell me that the person I was working for was very important and that I couldn't be here any more.

Yarl's Wood Immigration Removal Centre in Bedordshire. Photograph: Robert Oates/Alamy

"I told my friend all the people I worked for were professional, important people, so I didn't know who exactly it was. They told me: 'The next day you're going to find out in the news.' And the next day the news exploded everywhere – here, in Spain, in Colombia. With my name."

Acevedo sobs angrily. "They destroyed a family in one day. They destroyed a dream, they destroyed a home."

Back in 2010, she applied for indefinite leave to remain for the family, but was turned down because her daughter had returned to Colombia for two and half years as a child. She appealed and in February was awaiting another ruling. "I thought because I was a hard worker, maybe someone would recognise in court that I was no problem here," Acevedo says. She is still distraught that her daughter, who won a scholarship to study fashion at the Camberwell College of Arts, was unable to take the place up without British citizenship. "For someone who's so bright and intelligent, it's like cutting the wings of a bird."

Charming, funny and elegantly turned out, Acevedo must have delighted the middle-class professionals who paid her less than £10 an hour to scrub their toilets; they trusted her and were generally polite and friendly, she says. Generally she worked from 9am until 4pm, making an average of £200 a week. Since February she has searched online and discovered that her other former clients include a top civil servant. She says that Richard Heaton, the permanent secretary at the cabinet office, paid her £40 to clean his flat and iron his "very nice" shirts for four-and-a-half hours once a fortnight. She saw him infrequently, but claims he never questioned her right to work nor asked to see any proof she was allowed to do so. A cabinet office spokesperson told me: "Mr Heaton can confirm that Ms Acevedo provided cleaning services to him for four-and-a-half hours per fortnight, on a self-employed basis."

For all that she has been through as a result of her connection with Harper, Acevedo maintains a surprising level of discretion; when I ask how many bedrooms his flat had, she refuses to answer on the grounds that this is too intimate a question.

Indeed, when the news of Harper's resignation first broke, it was his future, rather than her own, she was most concerned about. "I felt guilty, I started screaming and saying: 'I'm sorry Mr Harper'," she says. "Initially I was like 'I've ended Mr Harper's life'. Now I'm realising his life hasn't ended, but mine has. He has a new job; I haven't got anything.

"What makes me sad is that there are thousands and thousands of people in this country in the same situation I was in [without papers allowing them to work]. If I hadn't worked for somebody so important there wouldn't have been such a scandal."

The precise number of illegal immigrants in the UK is unknown, but a 2009 London School of Economics study commissioned by the London mayor, Boris Johnson, estimated the number of "irregular residents" – migrants and their children – at 618,000, with more than two-thirds, 442,000, in the capital. Paid low wages, cash in hand, they work in pubs, hotels, restaurants and construction, or clean offices and flats.

Knowing how common her position was, Acevedo didn't fear she would be caught. "I never felt worried because I just thought 'I'm working'," she says. "I thought there must be so many people doing the same thing, I didn't see anything wrong with it.

"Everyone has the right to opportunity. And if they would give me my papers I would pay my taxes and that would contribute to the economy." The LSE study backs her up: it found that an amnesty for irregular migrants could provide a £3bn boost to the economy.

"It seems the system hurts people who are just trying to survive and have done nothing wrong," Acevedo says. "The laws need to change."

'I felt like the loneliest person in the world. I missed my job, so I would get on the bus in the morning with nowhere to go'

She remembers seeing the now-infamous advertising vans telling illegal immigrants to "go home", for which Harper was responsible, and wondering how she was meant to do this. Her husband, who had joined her in England but from whom she was now separated, had been attacked on the street and left seriously ill from a head injury. She became his carer until he decided to return to Colombia voluntarily. "There are thousands of people out there for whom it's just impossible to go home," she says.

What does she think now that she knows the vans were Harper's policy? "I'm very disappointed," she says, with a laugh, "when I remember the love I used to iron his shirts with."

Acevedo was forced to stop working after Harper resigned, hunkering down and surviving thanks mainly to donations made to a campaign led by Trenton Oldfield, who successfully resisted deportation to Australia after being arrested for jumping into the Thames to disrupt the 2012 Oxford-Cambridge Boat Race, and his wife Deepa Naik. They got involved after reading about the case and seeing the similarities with their own legal battle.

Mark Harper, former immigration minister, now minister for disabled people. Photograph: Adrian Sherratt/REX

"I felt like the loneliest person in the world," she says. "I locked myself up in my room and I cried and cried. I missed my job, so I would get on the bus in the morning with nowhere to go. Whenever I heard sirens outside I was scared they were coming to get me." Close friends, unnerved by what had happened to her, stopped contacting her. She has heard nothing from the Harpers.

Acevedo has not seen her daughter since she was arrested, and does not want her to come to visit her at Yarl's Wood.

She left the ceremony room when asked to do so by a member of staff, never expecting what was outside the door. "I saw huge men in uniforms," she says. "One of them grabbed me so hard it made a mark. He said: 'You know why we're going to arrest you?' I said I didn't. He said: 'Because you are an illegal.'

"It was a horrible thing to do to a mother, taking her out of her daughter's wedding. It's the most humiliating thing in the world."

She fears for her safety in Colombia, a country where, as she puts it, "anything can happen". If the deportation bid is successful, she will live with her 85-year-old mother, who knows nothing of her troubles in the UK. "I've spoken to friends back home and they all say there's nothing to do there for work. At my age it will be very difficult for anyone to employ me."

What has she enjoyed about life in the UK in happier times? "I've seen other people who do have their documents in order and the opportunities there are to study, to have a good job, a dignified life," she says. "There are open doors so you can progress as a person. I've thought about doing volunteering with older people.

"Before I came here, I thought: 'Wow, it's just a paradise, full of opportunities.' I got here and just felt humiliation at the things I've had to do and the way they're treating me now."

Before leaving Yarl's Wood I ask about her hopes for the future if she does return to Colombia. For the first time she is lost for words.