Ostracised, vulnerable and frightened, she wandered the streets in south-eastern Nigeria, sleeping rough, struggling to stay alive.
Mary was found by a British charity worker and today lives at a refuge in Akwa Ibom province with 150 other children who have been branded witches, blamed for all their family's woes, and abandoned. Before being pushed out of their homes many were beaten or slashed with knives, thrown onto fires, or had acid poured over them as a punishment or in an attempt to make them "confess" to being possessed. In one horrific case, a young girl called Uma had a three-inch nail driven into her skull.
Yet Mary and the others at the shelter are the lucky ones for they, at least, are alive. Many of those branded "child-witches" are murdered - hacked to death with machetes, poisoned, drowned, or buried alive in an attempt to drive Satan out of their soul.
The devil's children are "identified" by powerful religious leaders at extremist churches where Christianity and traditional beliefs have combined to produce a deep-rooted belief in, and fear of, witchcraft. The priests spread the message that child-witches bring destruction, disease and death to their families. And they say that, once possessed, children can cast spells and contaminate others.
The religious leaders offer help to the families whose children are named as witches, but at a price. The churches run exorcism, or "deliverance", evenings where the pastors attempt to drive out the evil spirits. Only they have the power to cleanse the child of evil spirits, they say. The exorcism costs the families up to a year's income.
During the "deliverance" ceremonies, the children are shaken violently, dragged around the room and have potions poured into their eyes. The children look terrified. The parents look on, praying that the child will be cleansed. If the ritual fails, they know their children will have to be sent away, or killed. Many are held in churches, often on chains, and deprived of food until they "confess" to being a witch.
The ceremonies are highly lucrative for the spiritual leaders many of whom enjoy a lifestyle of large homes, expensive cars and designer clothes.
Ten years ago there were few cases of children stigmatised by witchcraft. But since then the numbers have grown at an alarming rate and have reached an estimated 15,000 in Akwa Ibom state alone.
Some Nigerians blame the increase on one of the country's wealthiest and most influential evangelical preachers. Helen Ukpabio, a self-styled prophetess of the 150-branch Liberty Gospel Church, made a film, widely distributed, called End of the Wicked. It tells, in graphic detail, how children become possessed and shows them being inducted into covens, eating human flesh and bringing chaos and death to their families and communities.
Mrs Ukpabio, a mother of three, also wrote a popular book which tells parents how to identify a witch. For children under two years old, she says, the key signs of a servant of Satan are crying and screaming in the night, high fever and worsening health - symptoms that can be found among many children in an impoverished region with poor health care.
The preacher says that her work is true to the Bible and is a means of spreading God's word. "Witchcraft is a problem all over Nigeria and someone with a gift like me can never hurt anybody," she says. "Every Nigerian wants to watch my movies." She denies that her teachings and films could encourage child abuse.
One British charity worker is fighting to help the children stigmatised as witches. Gary Foxcroft, 29, programme director for the UK charity Stepping Stones, Nigeria, first came to the country in 2003 to research the oil industry for his masters degree. But he was so shocked when he learned about the children's plight that he decided to help raise money for the refuge - the Child Rights and Rehabilitation Network (Crarn) - and try to persuade the parents to take their children back. He has also helped to build a school for the children who are refused places at local schools.
"Any Christian would look at the situation that is going on here and just be absolutely outraged that they were using the teachings of Jesus Christ to exploit and abuse innocent children," says Mr Foxcroft whose expose of what he describes as "an absolute scandal" will be screened in a Channel 4 documentary on Wednesday.
The Niger Delta is an oil-rich region but the wealth does not reach the people who live there. The locals blame their hardship on the Devil but international analysts point to the oil industry's large-scale contamination of air, land and sea.
In the documentary, the charity worker visits one of the pastors, a man who calls himself "the Bishop" and who claims to be able to drive evil spirits out of "possessed" children. At his church in Ibaka, the Bishop pours a homemade substance called African mercury, a potion of pure alcohol and his own blood, into the eyes of a young boy lying on a table. "I want this poison destroyer to destroy the witch right now, in Jesus' name," he says.
The priest charges £170 - in a country where millions of people are forced to live on less than £1 a day - for "treating" a child every night for two weeks, and holds them captive until the bill is paid.
He has recently refined his techniques for dealing with child witches. "I killed up to 110 people who were identified as being a witch," he says. He claims there are 2.3million "witches and wizards" in Akwa Ibom province alone.
The children's shelter was started five years ago when Sam Itauma, a Nigerian, opened his house to four youngsters accused of witchcraft. Today, he and his five staff are caring for 150 youngsters. "Every day, five or six children are branded as witches," he says "Once a child has been stigmatised as a witch, it is very difficult for someone to accept that child back. If they go out from this community... there is a lot of attacks, assault and abuses on the children." Children often arrive at the shelter with severe wounds, but few clinics or hospitals will treat a child believed to be a witch.
"Christianity in the Niger Delta is seriously questionable, putting a traditional religion together with Christian religion - and it makes nonsense out of it," he says. "If you are not rich and don't have anything to eat, you look to blame someone. And if you don't get anything, you blame it on the witches."
Christians have been in Nigeria since the 19th century and the Niger Delta area claims to have more churches per square mile than any other place on Earth. The vast majority of the country's 60 million Christians are moderate, but an influx of Pentecostals over the past 50 years has led some churches to be dominated by extremist views. Five years ago, the Nigerian government passed a Child Rights Act, which made abuse illegal, but not every state has adopted it.
At the refuge, a baby girl called Utibe and her five-year-old sister, Utitofong, are dumped at the gate by their mother because a "prophet" told her that Utitofong was a witch and had passed the spell to her sister. The mother, who spent four months' salary on an unsuccessful exorcism, left them at the centre because she feared they would be killed. The police are called but locals offer them no help.
Mr Itauma goes to the village to try and convince the locals to accept the daughters' return, but the older girl is threatened by a man with a machete. "Get away from our food - I'll kill you," he shouts. Utibe is allowed to stay, but the older girl has to go back to the refuge.
At the end of the film, Mr Foxcroft and all the "child-witches" stage a demonstration at the Governor's residence in the state capital, Uyo, and urge him to adopt the Child Rights Act." After four hours the Governor comes out and says the Act will be adopted. It has since been adopted, but so far not a single pastor has been convicted of any offence. And the rescue centre still takes in up to 10 children a week.
Mr Foxcroft took Mary back to her village where he was told that her father left a year ago to find work in Cameroon. A cousin says: "She is a witch, we don't want her here." Mary is now back at the refuge.