Mrisho, the youngest of five children, was in her final year of primary education and was hoping to become a teacher when her father, a struggling fishmonger, told her to prepare for her wedding and ready herself for a new life with a husband he had chosen for her - a man 24 years her senior.
"I was very shocked because I was too young and also I didn't want to get married since I was still at school. But I couldn't go against my father's wishes," she said.
Mrisho had always been viewed by her family largely as a financial asset. Her mother died when she was a toddler, but her father later married again, this time to a woman half his age.
"My dream was to become a teacher, but I could not fulfil it as I got married and became pregnant ... now I have a child it's unlikely I would go back to school," Mrisho told Thomson Reuters Foundation in an interview at Zinga village, near the historic town of Bagamoyo in Tanzania's Coast region (Pwani), where she is staying.
Mrisho's story is common among families of the Zaramo tribe in the impoverished village of Mlingotini, 15 km from Bagamoyo, where parents often marry off their daughters to get money or cows. A month before Mrisho's education was cut short, her classmate Zaituni was secretly removed from school and married to a 42-year-old man who turned out to be a polygamist.
"My teachers opposed the idea of me getting married, but my father was rather insistent," Mrisho said. "Whenever I told him I wanted to remain in school, he shrugged it off by saying he did not attend a single class himself yet he managed to produce children and have a family."
Unlike other weddings, which are often spiced up by traditional rituals known as Unyago - in which girls who have reached puberty receive training in childbirth and motherhood - Mrisho's was a completely private affair. She was wedded to a man she had never met before.
"I did not see the man until the very day he came to our home and took me away."
LEGAL AT AGE 14
In the Zaramo tribal tradition, when the man has paid his dowry, he becomes the sole custodian of the bride since she no longer belongs to her family.
Married life was difficult for Mrisho. Within a year she became pregnant, and there were complications.
"When I got pregnant I had severe stomach pains, but he accused me of faking the pains. He refused to take me to hospital and instead he gave me a concoction of herbs to drink," she said.
Mrisho had a difficult delivery. "I thought that was the end of my life, but (I survived) thanks to an elderly woman who came to my rescue and helped me deliver."
A year or so after her baby boy was born, Mrisho's marriage turned sour. "I decided to run away from him, but I could not go back home. I went to stay with my aunt who is living in Zinga."
Women's rights groups blame Tanzania's high rates of child marriage on the country's marriage law, which gives the courts and parents the discretion to marry off children as young as 14.
"Some parents are hiding under the shadow of this law and selling their daughters to get money or cows. We strongly condemn this behaviour," said women's rights activist Eddah Hawala of the organisation Kiota Women's Health and Development.
Hawala, whose agency helps marginalised girls, said early marriage exposes girls to the risk of contracting sexually transmitted diseases and death in childbirth.
"At the age of 14, a girl is still growing, and her body is not yet ripe for giving birth, so we consider it very brutal for a parent to marry off his daughter at that age," she said, adding that the marriage law should be changed as it undermines girls' rights.
A 2008 survey on child marriage carried out by Children Dignity Forum shows that child marriage is a big problem in Tanzania and is more prevalent in its Coast, Mwanza and Mara regions.
The survey found that child marriage was driven by factors including the desire of a girl's parents to get a dowry, especially when they are poor, and a lack of knowledge about the impact of such marriages.
Girls are more seriously affected by child marriage than boys, as they are more vulnerable to disease and can have complications during childbirth. For instance, obstetric fistulas - holes in the birth canal - are common among young mothers who give birth at home because they are too poor to attend health clinics, the survey showed.
World Bank data shows that 22.8 percent of girls aged 15 to 19 in Tanzania had children or were pregnant in 2010, while the adolescent fertility rate (the number of births per 1,000 girls aged 15-19) was 129, giving Tanzania the highest adolescent fertility rate in the world - a situation blamed to a large extent on early marriage and a high school dropout rate, the Daily News reported in April.
The Tanzania Media Women's Association (TAMWA), an NGO for women journalists, says there is a strong correlation between child marriage, school dropout rates, early pregnancy and HIV/AIDS and it estimates that between 20 and 40 percent of Tanzanian girls marry before adulthood.
In an interview with Thomson Reuters Foundation, TANWA activist Ananilea Nkya called on the government to enact a new law making it illegal for parents to force their children to leave school and setting a minimum age for marriage of 21, in the hope that girls will not have children until after they are married.
"At that age, the girl should have sufficient education to understand the intricacies of life," she said.
If the current rate of child marriage persists, more than 140 million girls around the world will become child brides between 2011 and 2020, the United Nations estimates.
Another reason for later marriage came in a report by the UN Population Fund in March, which said that girls who marry before the age of 18 run a greater risk of becoming victims of violence inflicted by their partner than those who marry later.