Sabika Sheikh’s excitement is palpable in the two-minute video, her brown eyes wide and her hands fluttering as she speaks.

“Hi guys, I’m Sabika,” she says. Cheery and energetic, the young girl had made the video to describe the moment her parents told her she was a finalist to be a youth ambassador in a US state department-sponsored study exchange that would take her thousands of miles away from her home in Karachi, Pakistan’s largest city, for a year.

“I didn’t believe it,” Sabika said. “They came into my room, and I was squealing, jumping like a madman. I prayed to God and thanked him a lot. Seeing those proud smiles on my parents’ faces, that was the best moment of my life.”

In the video, Sabika speaks in the chattering cadence of a teenage girl. Just a little more than a year after she posted that video on YouTube, Sabika, 17, was one of 10 killed in a mass shooting at a Texas high school.

On Wednesday, her parents joined the family members of some of the other victims in filing a lawsuit against the 17-year-old suspect’s parents, Antonios Pagourtzis and Rose Marie Kosmetatos. The suit alleges the parents were not only negligent in allowing their son to gain access to a shotgun and a revolver legally owned by the father, but in failing to respond to warning signs that their son posed a risk to others.

An attorney for the suspect’s parents had previously denied all allegations in an earlier court filing, before Sabika’s parents joined the lawsuit, arguing that the “mere fact of paternity or maternity does not make a parent liable to third parties for the torts of his or her minor child”.

But in adding their voices to the fight, Sabika’s family is ensuring that the gun violence and mass shootings that have become a tragically American phenomenon stay firmly in the international eye.

Guadalupe Sanchez, 16, cries in the arms of her mother, Elida Sanchez. Photograph: Michael Ciaglo/AP

“We trusted this country more than I think we should have,” said Shaheera Jalil Albasit, Sabika’s cousin. “We sent Sabika here as a guest. She was here on a cultural exchange, and she experienced the worst of the culture: the culture of gun violence.”

Sabika arrived in the United States in August 2017 as a youth ambassador for the Kennedy-Lugar Youth Exchange and Study Program. It was her first solo trip, and it was to be the longest amount of time she was to be away from her family, her cousin said.

She was placed with a host family in Santa Fe, Texas, 30 miles from central Houston. She enrolled in Santa Fe high school, and experienced typical American teenage life, dressing up for Halloween, going to prom with friends, volunteering at the library, and keeping score at high school baseball games.

“She was really thinking of this opportunity as the step a woman would take to show people that girls can travel alone, make friends across religions, across cultures, and do great things,” Albasit said. “I think that was her aspiration, coming back and sharing stories about what she did here. She was also excited about sharing the positives about Pakistan.”

Though Sabika loved her time in Texas and grew close with her host family, she was, in the last few weeks, “really missing home”, Albasit said. “She kept talking about going home to her mother, and going home. She started a countdown. Every day, she’d send a message home to Pakistan.”

On 18 May, Sabika posted one last Snapchat story: just 19 more days.

At 7.30am, the shooter, a fellow student, walked into the four-room arts complex and opened fire, killing eight teenagers and two teachers. Thirteen others were injured, some seriously.

According to court documents, Sabika and her classmates ran into a supply closet, where she hid behind a dresser. “The shooter … began shooting into the closets,” the filing reads. “He taunted the students who were hiding while he shot at them.”

Sabika sustained nine gunshot wounds. The suspect, Dimitrios Pagourtzis, was arrested and charged with capital murder but cannot face the death penalty because of his age.

Shooting suspect Dimitrios Pagourtzis. Photograph: AFP/Getty Images

Antonios Pagourtzis and Rose Marie Kosmetatos “knew that something was gravely wrong with their son”, but took no steps to get him help or prevent him from accessing firearms, the lawsuit alleges.

The shooter had a fascination with the Columbine shooting, and went out of his way to dress like the shooters: wearing a full-length black trench coat and combat boots to school – even in the Texas heat.

He was also fascinated by guns, in particular guns used by the Nazis in the second world war. On Facebook, he posted an image of a jacket with Nazi and fascist insignia, as well as artwork inspired by an electronic musician with a following among neo-Nazi groups.

The day after the shooting, the family said in a statement they were “as shocked and confused as anyone else”.

“While we remain mostly in the dark about the specifics of yesterday’s tragedy, what we have learned from media reports seems incompatible with the boy we love,” the statement read. “We share the public’s hunger for answers as to why this happened, and will await the outcome of the investigation before speaking about these events.”

Sabika’s family, who are represented by the gun policy reform group Everytown for Gun Safety, hopes the suit will force accountability on not just gun owners, but on people who ignore warning signs in their loved ones, even though they know of the risk they might pose to others.

“We believe that the shooter’s parents had multiple opportunities to stop what had happened, and they did not engage in anything,” Albasit said. “The motivation behind this lawsuit is that any gun owner in the US must feel an obligation when it comes to their weapons, not just in storing them safely, but in speaking up when they believe that someone around them is at risk of harming themselves or people around them.”

Sabika’s parents never imagined that anything like this could happen, her father, Abdul Aziz, said in a phone interview from Pakistan. “How can a parent even think about their child being injured or hurt or taken away forever?” he asked.

“It’s a very specifically American problem, this gun violence. But any manifestation of violence, especially targeted at children, should not be a reality. Children should not be stopped from pursuing education, no matter the reality. The reality must be corrected.”

Farah Naz, Sabika’s mother, said: “It’s a very dark place to be for the family.”

The sole light in that darkness, she said, is the duty they feel to deliver justice for their daughter. “We feel that we are accountable to Sabika every single day. We see her face in front of our eyes every day. Her voice, her sound, her laughter echo in our ears every day.”

Sabika wanted to be an entrepreneur and a diplomat. One of the last things she wrote to her mother was that she had “amazing daughters who will make you proud”. Sabika’s mother now mourns for the future that one amazing daughter will never have.

Sabika’s parents speak Urdu, and the phone interview was conducted through a translator. But when asked what it was about his daughter that he missed the most, Abdul Aziz answered immediately in English.

“Everything,” he said. “Everything. Everything.”