"I was raped!" she said on the stand when a defense lawyer suggested she had sent conflicting signals to the defendant.
"I was violated in so many ways," she said in tears. "Of course, I was traumatized. I'm sorry. I'm sorry. I was traumatized in this retelling."
At the conclusion of her testimony, the young accuser left court crying. It was the third day of a trial that has brought unwanted attention to the elite St. Paul's School in Concord. Graduates have included six congressmen, more than a dozen American ambassadors and U.S. Secretary of State John Kerry.
The accusations have shed light on a campus tradition known as the "Senior Salute," in which seniors try to have sexual encounters with as many younger students as possible before graduation.
Owen Labrie, 19, who has pleaded not guilty, is being tried on charges that include the rape of the 15-year-old student on the sprawling campus in May 2014 -- just days before his graduation.
On the stand, the girl said she agreed to meet Labrie and accompany him to a machine room. When they kissed, she did not object, she testified. But soon he began to grope her. He bit her chest and tried to remove her underwear, she said.
"I said, 'No, no, no, keep it up here,'" she testified, signaling above her waist. "I tried to be as polite as possible."
The girl said she closed her eyes when he penetrated her with his fingers. Later, he raped her.
"I didn't know what else I could do," she said. "I already said no ... I felt like I was frozen."
Labrie looked down at the defense table during much of her testimony, occasionally jotting down notes.
Asked by defense lawyer J.W. Carney if she laughed during the encounter, the girl described it as nervous laughter.
Carney pressed her about emails she exchanged with the defendant before and after the encounter. He challenged her credibility, noting she told an investigator she was "excited to have attention" from Labrie.
She burst into tears as Carney pointed out discrepancies in her account.
"I was raped!" she said during an emotional day on the stand.
Labrie used the Internet and Facebook to entice and lure the girl into a sexual encounter, Deputy Merrimack County Attorney Catherine Ruffle said during her opening statement Tuesday. He allegedly told friends he had sex with the girl.
The victim suffered injuries "consistent with a sexual assault," Ruffle said. DNA evidence matched the defendant, she said.
"Did you use a condom?" the alleged victim asked Labrie in a message, according to Ruffle.
"Are you on the pill? I think you're OK. I put it on halfway through," the defendant allegedly wrote back.
Carney said the "Senior Salute" is a decades-old school tradition that could involve "kissing or hugging." Some salutes are not sexual in nature.
"If they kiss a freshman, sophomore, or junior, it could be a 'Senior Salute,'" he said. "It was a competition. How many girls can I have kiss me or be with me?"
Being invited to participate in the salute was a "source of pride" for younger students, Carney said.
Carney said his client told police he kissed and hugged the victim but did not have sexual intercourse with her. He read messages that he said proved the girl willingly participated in the encounter.
"There's a door here that's been locked since before we were born," Labrie wrote in one message. "If you want the definition of bittersweet, think of me spending three years trying to open it, but only having three days."
She declined at first but then changed her mind.
"Only if it is our little secret," she wrote.
"Not a soul needs to know," Labrie replied.
In another message, he wrote: "You're a gem. Let me know if there is anything I can do."
"You're not too bad yourself. I will. I also lost my earring up there. haha," she responded.
The defense contends the defendant did not sexually penetrate the girl and that the encounter was consensual.
In a statement, St. Paul's Rector Michael Hirschfeld said, "We do not tolerate conduct that is at odds with our commitment to a safe and welcoming environment for everyone in the St. Paul's School community. Current allegations about our culture are not emblematic of our school or our values, our rules, or the people who represent our student body, alumni, faculty and staff."
The residential Episcopal high school, where tuition is $52,000 a year, was founded in 1856.