When Khadija was 10 years old, she begged her mother to be circumcised. "All my friends have had it done and I don't want to be the odd one out," she pleaded.

"My mum never gave a reason why she kept saying no, but once I'd had it done I understood why she was reluctant," says Khadija. She was 11 and still living in war-torn Somalia when her mother gave in and Khadija underwent female genital mutilation (FGM).

In a terrible way, the war may have helped. "After a girl has been cut, they get stitched up and then things are opened up again on her wedding day. I didn't have the worst kind done because, with that one, they have to tie your legs together afterwards to help the wounds heal and make the flesh come back together. I needed to be able to use my legs as we had to run away because of the war."

However, the "less invasive" version that Khadija, now 17, underwent was excruciatingly painful. Using an assumed name to keep her identity private, she describes the traumatic event played out as her mother stroked her hair. "Faridad" (good girl), said an old woman who appeared holding in her hand a broken razor blade. She bent over me, then an explosion of pain erupted. It felt like I was being skinned alive with the breath driven out of my body. The hot, searing pain forced a scream from my throat, my legs coiling into a spring that made the grip of the two women tighten even more. Most of the women who carry out the initiation are not well educated and sometimes end up cutting a vein, causing the girl to bleed to death."

Although she now shudders at the thought of what was done to her and her friends, she believed it was just something girls had to go through before they could join the "circumcision club".

She changed her mind about FGM after she fled Somalia two years ago and claimed asylum in the UK. She arrived with her aunt and the pair were sent to Yorkshire by the Home Office, which is providing them with support until their asylum claim is determined. Khadija started school and assumed that, as in Somalia, female circumcision was the norm for girls in the UK. But after asking one of her friends if she had been cut and receiving a blank stare she began to realise that not only had none of her friends been circumcised but most girls of her age did not even know that this practice existed.

"In Somalia, it's taboo to go against female circumcision. But when I came to England I started to realise that the kind of tradition we were abiding by is not the path that human beings should follow," she says.

Supported by her teachers, first at her secondary school and now at her sixth-form college, she is speaking out to her fellow students about the horrors of FGM, as well as using articles such as this and Facebook to raise awareness.

"There are thousands of girls living in the UK who have undergone FGM. Much more needs to be done to raise awareness about this and prevent it happening to more girls," she says. "I want to help other girls who might be at risk of FGM by condemning it as much as I can."

Last month, the United Nations General Assembly unanimously passed a resolution banning the practice of FGM. Between 100 million and 140 million women and girls are affected worldwide, with an estimated three million girls at risk each year and 8,000 girls a day undergoing the procedure. FGM is common in 28 countries in Africa as well as in Yemen, Iraq, Malaysia, Indonesia and among certain ethnic groups in South America. Girls in diaspora communities are also at risk of being subjected to FGM.

In the UK, the Crown Prosecution Service has announced plans to crack down on those who compel young girls to undergo FGM. It has been a criminal offence for 30 years but there has never been a successful prosecution. About 24,000 girls under the age of 15 in the UK are thought to be at risk of FGM. Another 66,000 have already suffered it.

Most do not want to speak about such a personal event. Yet Khadija, while researching inspirational Somalians for a school assignment, came across the supermodel Waris Dirie, who has tirelessly campaigned against FGM and has written an international bestseller about her own experience of this practice. The book was made into a film, called Desert Flower. "Waris Dirie inspired me to speak up at my school against FGM. My dream would be to meet her," she says.

One of Khadija's GCSE teachers is hugely impressed by her decision to raise awareness about FGM. "She hasn't seen her parents for years – she was kidnapped by a terrorist group in Somalia. She did a full set of GCSEs after just two years in the British education system and she lives with the worry that she might be detained and deported at any point. What she's doing is phenomenal," he says.

Although Khadija doesn't know what has happened to her parents, she hopes they will approve of her stance. "My father often used to say, 'When you have an education you carry the whole world in your hands'," she says. "If I was still in Somalia I wouldn't even think of speaking up about these things because my life would be at risk. But now that I'm in a free country, where people can be open, I want to try to help girls who could lose their lives from FGM. Girls who don't have a choice about whether or not they are cut."