(CNN) Spring break is over and campus is bustling, but all Sonita Alizadeh can think of is the brutal murder of a young Afghan woman.

Surrounded by the excited chatter of reunited peers, Sonita is consumed with news coming from her home of Afghanistan, where a 27-year-old named Farkhunda was publicly beaten and killed in the streets of Kabul in March.

Halfway across the world, from a small preparatory school in Utah, Sonita feels helpless, distraught by news of another Afghan woman deprived of her livelihood. Rather than sleep or focus on school, she turns to the only activity that brings her comfort: she writes a song, goes to the school's music studio, leans her face into a microphone, and raps.

Why are you dragging me like this? Showing your power over my wounded body?

For God's sake, listen to me first! Don't beat me with your fists, give me a chance!

Sonita goes back to her dorm and, for the first time in days, sleeps soundly.

Sonita Alizadeh raps into a microphone at a music studio on her campus at Wasatch Academy.

Escape to Iran

A refugee from a devout Muslim family, Sonita has been in the United States for close to a year. And though the mountains of central Utah resemble the country she left behind, life here is starkly different.

Here, she feels safe. She doesn't fear Taliban fighters or aerial bombardment. She can get a formal education and learn English, history, math and music. And perhaps most importantly, she can be single. Had her life gone as her mother planned, she says she would be married by now, sold to the highest bidder.

"I don't like to think about that," the 18-year-old says through a small smile. "I ran away from it."

From fleeing the violence in Afghanistan to escaping a forced marriage as a teenager, Sonita -- a petite woman, with long black hair and huge, beaming eyes -- exudes a calm confidence for someone who has had so much to run from.

Sitting in her cozy dorm room, Sonita recalls her childhood in Herat, growing up under the oppressive rule of the Taliban. Haunted by the ashen faces and long, scraggly beards of Taliban soldiers, Sonita says she was always hungry as a child and always afraid. "They were awful," she says. "I still see them in my dreams."

She remembers the perilous journey from Afghanistan to Iran -- where her family fled in hopes of a better life. She says a Taliban soldier demanded money from her family for safe passage and threatened to kidnap her and her sister. It was terrifying, she says. It was also the first time she was ever referred to as property.

From rags to rapping

In Iran, Sonita delved into poetry as a teenager. Without proper identification, she never had access to formal education, so she cleaned bathrooms at a non-governmental organization for Afghan refugees while learning the basics of how to read and write. She watched music videos on TV to pass the time. In the comfort of the musical stylings of Iranian rapper Yas and Eminem, she learned lyrical style and cadence.

Sonita soon began writing her own songs. And though she struggled to find studio space to record her music -- singing solo as a female is illegal in Iran without special permission from the government -- she managed to rap in secret with the help of a few defiant music producers. Her determination even drew the attention of a documentary filmmaker who began following her story.

She rapped about the war in Afghanistan, and the challenges she faced as a refugee, a child laborer and especially as a female.

In the name of this pen that is my weapon, and my voice that is the voice of my generation

Let this story tell you about the truth, the story of defenseless women of Afghanistan

She rapped about her friends, who often came to school with bruised faces and broken spirits after long nights of arguing with their families. They would beg their parents not to sell them, not to marry them off, to let them decide their own future, Sonita says. But to no avail. One by one, she watched her friends disappear to get married and have children. "Children having children," she adds. She says she saw girls as young as 12 married off to much older men.

Such is the practice in traditional Afghan culture, where a young girl's bride price can fetch a family thousands of dollars, according to the United Nations.

While Afghan civil law says that a girl cannot marry until she is 16, or 15 with her father's consent, the United Nations claims that some 15% of Afghan females are married before age 15. Of all Afghan marriages combined, roughly 60 to 80% of them are forced, according to the United Nations, citing numbers from the Afghanistan Independent Human Rights Commission.

Through her lyrics, Sonita tried empowering her friends to protest their parents' wishes. Documentary footage from the upcoming film "Sonita" shows her at the NGO, rapping to a young friend who is facing the prospect of being sold as a second wife to man in his 30s for $4,000.

There's noise, dad is coming, we'll make big bucks for our daughter

No more school for you girl, it's not your track

I feel I had reached the end of the line

But I want my right and will start to fight

"It's what I would like to tell my father," her friend says through tears.

In 2014, Sonita's music put her on the world map. From Tehran, she entered a U.S.-funded competition to write an anthem to get voters in Afghanistan to the polls. Her music video challenging young Afghans to stand up for their country won and she received a $1,000 prize.

She sent the money to her mother, who had moved back to Afghanistan. Sonita says her mother was pleasantly surprised to see her daughter contribute. "She understood that I can make money like a boy."

'There's a man, and he's waiting for you'

Months before Sonita won the competition, at a transit station in Tehran, Sonita bolted towards a large, grey charter bus, threw her arms around her mother and burst into tears. Her mother, donning a long black chador -- a traditional garment for Muslim women -- also began to cry. It had been three years since they had last seen each other.

But what Sonita thought was a casual visit by her mother came with an agenda. A few days into her visit, her mother told Sonita, then 16, that she must return to Afghanistan with her. "She said, 'there is a man, and he waiting for you," she recalls.

Sonita's brother needed a $7,000 dowry for his soon-to-be bride. Her mother thought she could get $9,000 for selling Sonita into marriage.

"I asked her, 'How can you sell your daughter?'" she exclaims. "She said it's tradition in our country."

Indeed, the tradition of a bride price is practiced throughout the developing world, explains Noorjahan Akbar, an outspoken women's rights activist. But for poorer families, Akbar says, it often translates into a practice that can harm young girls.

She says girls are already considered an economic burden, as female employment is particularly taboo in Afghan culture. Plus, Afghan families are big -- with the average number of five children for one Afghan family, according to data for the World Bank.

"So the tradition repeats itself," Akbar explains. "Families are left with the burden of paying for wives for their sons, so they have to use their daughters."

'Daughters for sale' debuts

Devastated, Sonita responded the only way she knew how: with a rap song. With the help of an Iranian filmmaker, she made a music video called "Daughters for Sale." In it, she dons a white wedding dress against a black background. With painted-on bruises and a bar code across her forehead, she pleads into the camera to not be sold, to be considered more than a price tag.

Let me whisper to you my words

So no one hears me speak of selling daughters

My voice shouldn't be heard, as it's against sharia

Women must remain silence, this is the tradition of our city

She posted the video to YouTube, where it has since been viewed close to 75,000 times.

"People love the video," Akbar, also an Afghan, says. It really resonates and "has been shared very widely among Afghan women."

A few weeks later, Sonita was contacted by the Strongheart Group, an organization that helps individuals directly impacted by social issues tell their story.

"She had passion and drive," says Zoe Adams, chief executive officer of the organization. "We knew we could help her achieve her dreams to get an education, develop as an artist and be a voice for girls being forced into marriage."

They offered to sponsor a student visa for her to come to the United States, where she could attend Wasatch Academy on a full scholarship. Finally, she could get a formal education at a high school. And she wouldn't have to worry about being sold.

"We saw a lot of potential in Sonita," says Joseph Loftin, headmaster of Wasatch Academy. "We thought she could be a very unique voice for our student body."

New song, new start

Sonita, then 17, jumped at the offer, but didn't tell her mother, scared of what she might say. It would take months for Sonita to get her passport and visa straightened out. She arrived in the United States in January. A few weeks later, she arrived at the Wasatch Academy campus, and finally called her mother to tell her where she was.

She was angry, Sonita says. She told her to keep her hijab on, and come visit as soon as she could. But her mother adjusted, she says. And even became happy for her once Sonita was able to send money home following her first concert in May. Now, Sonita says her family encourages her music. "They're even waiting for my new song."

As for almost being sold, Sonita say she doesn't hold it against her mother. "She loves me, I know that," she says. Her mother, herself a child bride, didn't meet her husband until the wedding day. She was simply repeating the cycle, Sonita says.

"The older generations, they are teaching us these old traditions," she says. "But we can change them. Not all of them. But some."

Sonita enjoys life in the United States. She hopes to extend her student visa to attend college after she graduates in two years. She loves the friends she's made on campus. And she loves learning English, as it allows her to communicate with people all over the world.

But she ultimately wants to return to Afghanistan as a rapper for women's rights. She knows it's dangerous to be a female activist in a deeply conservative country, but, she says, "my country needs a person like me."

"My family, they changed their minds," Sonita says. "If I can change their minds with my music, then maybe I can change the world."