The mere suspicion of witchcraft was enough to see her and 80 other suspected witches expelled to a scruffy camp of mud huts on the fringes of the town of Gambaga in northern Ghana.
''It is the work of the devil. I can't say I have ever practised it myself,'' says Mariama, who has lived in the camp for about 10 years.
Hundreds more women accused of witchcraft live in similar camps in the cocoa- and gold-producing West African country.
Belief in witchcraft remains widespread in Africa, the world's poorest continent, where Christianity and Islam rub shoulders with animist religions, and where witch doctors wield great power in tribal societies.
In the poor, dry savannah of northern Ghana, the heat shimmers under a pale blue sky and allegations of witchcraft bubble up as readily as tar in the tropical heat.
Like the witches' trials in Salem, Massachusetts, in 1692 or the Cold War persecution of alleged communists in 1950s America, the fate of a suspect often hangs on the word of another.
Death, illness, dreams, superstition or even visible signs of success may be enough to provoke accusations of sorcery.
No matter how hard the allegation is to prove -- or how hysterical the accuser -- the fact that witchcraft is virtually impossible to disprove means many women are forced to live outside their communities, some for as long as 30 years.
Some are brought to the witch camps by their families. Others flee there from their homes and villages, fearing a beating or worse. Most of the occupants of the camps are women, although there are some men.
Human rights campaigners say camp populations are declining, thanks to efforts by concerned agencies to reintegrate the women into society and fight the influence of witchcraft.
''People are becoming better aware that these issues are not just metaphysical but also a human rights issue,'' said Richard Quayson, deputy commissioner of the Commission on Human Rights and Administrative Justice (CHRAJ), Ghana's leading human rights organisation.
''People don't tend to attack those who leave the camp and go back into society,'' he added.
MALIGN FORCES Yet a belief in malign spiritual forces remains strong in Ghana, especially in poor rural areas, and some say the camps will exist for many years to come.
Mariama Alidu's own brother accused her of witchcraft, following an argument over her daughter's choice of fiance.
When his own daughter fell ill, he blamed his sister and Mariama was taken to the Gambaga witch camp. At first, she thought she was just going on a trip. Only when she arrived did she realise where she was and what was happening.
Gambaga's local chief, who lives in a larger mud hut than the others, requests money from visitors interested in meeting him and talking to the witches.
''In the olden days, when our forefathers were not yet born, when someone was suspected of being a witch, the fellow was killed. It is to eliminate this act of killing, that is why they are in the camp here,'' he said through an interpreter.
''If you have a witch in your community, you feel the witch is disturbing you. We can keep them here.'' The chief said the ''witches'' worked the fields with his wives, and in return he gave them food and shelter. Many also lived on charitable donations.
PRICE OF SUCCESS For many of these outcast women, their crime may be a quarrel with a daughter-in-law or simply that they have passed child-bearing age.
In places where medical knowledge is scarce, illness is also often seen as having a spiritual or malignant cause.
Even an elderly woman's appearance in a dream can be taken as a sign of her malevolent intent.
In some cases, witchcraft offers an easy explanation as to why one person is successful and another is not.
''In cases where successful women, brilliant women, have gone beyond the confines of their status as women, witchcraft is used as an explanation,'' said Dr Abraham Akrong, of the University of Ghana's Institute of African Studies.
His own mother, a successful businesswoman, feared buying land in case people attributed her success to witchcraft.
Ironically, the rise in Ghana of charismatic Christian churches, with their focus on the fight against evil, has intensified fear and belief in witchcraft, even among educated people, Akrong said.
For Alidu, the hut she shares with two others is likely to remain her home until her family is willing to take her back.
Over the years, she has visited her children, who do not believe she is a witch. Too old to work on the chief's farm, she relies on food brought to her by other residents.
Asked if she is angry with the brother who cast her out, she said: ''We were born of the same woman. I don't understand why he should accuse me of being a witch when our mother wasn't a witch.'' REUTERS AKJ BD1334