One day when it was raining some people came with machetes and the killings began, she says. Her parents, who were farmers, her brothers and many others were killed. Everyone, except her two uncles. She did not see the murders because, like so many others who escaped the interhamwe, she was hiding in the bushes, literally shaking in terror. But she heard everything and later saw their mutilated corpses. She can still vividly recall the smell of the many dead bodies she saw and can still hear the sounds, especially at night.
While the killings were continuing she stayed alone and afraid in the bushes for two nights, until the killers left.
"When I was hiding, ants were crawling all over me. I tried to lie still, not to move, because I was afraid they would kill me if I moved. I lay so still that my muscles began to ache."
Mary is one of around 70,000 children who have received counselling to try to help them recover from the terrible events of last year. Under a programme set up jointly last September by UNICEF and the new government, more than 2, 500 professionals and community leaders have been trained to give counselling, just under half of them teachers.
A pilot survey among 62 children (half in orphanages, the rest in their own families or foster homes) by UNICEF's trauma recovery team shows that almost two-thirds were present at mass killings. More than half actually saw people being injured or killed. Mary's experience of family bereavement and being forced into hiding was also shared by the overwhelming number of children (see table, left).
According to Dr Leila Gupta, project officer for UNICEF's psycho-social trauma programme, most children caught up in massacres are suffering the major symptoms of post-traumatic stress disorders - principally flashbacks, giving them total recall of what they saw, heard, smelled or felt at the time.
"Children have witnessed their mother or father macheted, decapitated or beaten to death. They try to stop the flashbacks, the bad memories and blot them out. But the trauma keeps recurring." she says.
Other common symptoms include nightmares and eating disturbances, either not eating or over-eating. "One of the symptoms teachers will notice is children who cannot concentrate because they are constantly trying to shut images out of their minds. In particular young boys can become aggressive, irritable, jumpy, withdrawn socially. They don't want to play with their friends and they become loners."
The symptoms. says Dr Gupta, are familiar to many survivors of the Nazi Holocaust, some of whom still get sweating palms if they hear a knock on the door because they think it is the Gestapo.
"Many of these children had to hide under dead bodies, in banana plantations, surviving on rain water, afraid to move for fear that the interhamwe would see them."
The role of teachers is particularly important in helping children overcome the trauma. With so many who have lost parents or elder sisters and brothers teachers may be the most important role models in their lives.
Dr Gupta has written a children's book to help teachers and parents deal with the feelings children are experiencing. Drawing from the experiences of children who have received professional counselling, it sets out to explain that bad memories, nightmares and inability to concentrate at school are normal for people who have experienced massacres.
Normality is a difficult concept to come to terms with for most Rwandans, even as the outward signs of recovery - the first harvest, the sound of children singing in school, the bustling markets - are apparent.
Radio Rwanda, hi-jacked by the extremists and used to exhort ordinary people to become killers at the height of the slaughter, is now being used to make parents and foster-parents more aware of the effects of trauma on their children and, very often, themselves. A pioneering national trauma recovery centre, staffed by native Rwandans with specialist help from UNICEF and other international agencies, has just opened in Kigali, and will concentrate on clinical treatment for severely traumatised children and their families and be a source of valuable research.
The importance of recovery, in mental health and outlook no less than in educational and economic terms, is seen as crucial to Rwanda's long-term prospects.