New York(CNN) Daniela, the second of four children from an affluent family in Mexico, was looking forward to attending an elite high school in Switzerland when she says her life took an unexpected turn.

The summer before she was to leave, her father sent her to a course created by self-described self-improvement guru Keith Raniere in Monterrey, near her hometown.

Despite being an academically advanced student, she says she dropped out of school and joined Nxivm, Raniere's secret society in Albany, New York, with the support of her parents. She says she was encouraged by Raniere to persuade her younger siblings to join her, a move that enabled Raniere allegedly to rape her 15-year-old sister.

Daniela shared her harrowing account in a Manhattan courtroom Thursday, where Raniere is standing trial on charges including racketeering, sex trafficking, sexual exploitation of children and human trafficking, among other offenses. She was identified in court only by her first name.

Daniela says she wishes she had done more to protect her sister. And she's ashamed to admit that she initially reacted to the news of her sister's interactions with Raniere with jealousy.

"I deeply regret that I didn't at that moment get my sister out of there," Daniela said Thursday, tearing up on the witness stand.

The founder of Nxivm, Raniere is accused of manipulating and grooming Daniela and other young women as "slaves" for his financial benefit and sexual pleasure with the help of an inner circle of women that included actress Allison Mack and Seagram's heiress Clare Bronfman.

Raniere's defense has argued his relationships with Nxivm followers were consensual.

Daniela's testimony extended the scope of the accusations to Mexico, where Nxivm had a center. There, she said she attended the 16-day intensive course that changed the arc of her life.

The indoctrination begins

Daniela said she was 16 in 2003 when she started classes at the center as a gift from her father, an acolyte of Nxivm's Executive Success Programs.

Her father and other Nxivm members told her that Raniere was a "scientist and the smartest man in the world," she said.

The class taught a mathematical equation that purported to prove that the world was going to end in 10 to 15 years, she testified. She was told that her efforts to better the world were pointless because the only way to change the world was through ESP.

Toward the end of the course, Daniela started contemplating leaving school to work for Nxivm at its headquarters in Albany.

Lauren Salzman, Raniere's second-in-command, told Daniela she could help the mission, Daniela testified. Salzman is a co-defendant in the case who pleaded guilty to racketeering and racketeering conspiracy charges.

Daniela's parents brought her to Albany, she testified, where she ended up sharing an apartment with other adults while she was to learn computer programming. But she never did.

She was paid a couple of times but then told she couldn't be paid because she didn't have a work visa, she said. She cleaned offices to stay busy.

A relationship turns sexual

Eventually, Raniere's interactions with her became flirtatious, when she was 17 and he was in his 40s, she said.

"I believe he was grooming me. The truth is by 2003, I had never been kissed, and I didn't have any sexual contact."

The first time they kissed, she said they were alone in an office. She felt uncomfortable but also flattered.

"I feel special. I feel chosen," she said.

When he started talking about sex, he said she was too young and she needed to lose 20 pounds, Daniela testified.

Their first sexual encounter was a few days after her 18th birthday, she said.

In a building for one of his failed businesses, he performed oral sex on her on a dirty mattress in an office, she said.

She insists he did not penetrate her, although she says he told her that he did.

Secrets emerge

As the relationship continued, Daniela said she performed oral sex on him daily.

He told her that he could fix someone's flaws by having sex with them, she said. He also told her that women claimed to see blue lights by swallowing his semen.

Eventually, she said she found out her sister Mariana was also involved with Raniere.

One Christmas, she said Raniere brought both sisters into a home and began kissing Mariana and touching Daniela. Both sisters started crying, she said, and they never spoke about it again.

"It felt dirty. It was wrong," she said.

When her visa to the United States was revoked, Daniela said Raniere devised a plan for her fly to Canada where she wouldn't need a visa. Another follower, Kathy Russell, met her with a fake ID, and they crossed the border together.

Daniela said Raniere would try to coax her into having sex with him and Russell to return the favor.

"I felt that because she brought me over, I felt like I owed them," she said.

More siblings arrive in Albany

In 2003, Daniela said her teenage sister and brother visited Albany for part of the school year there, then returned to Mexico.

Raniere urged Daniela to coax them to return for Nxivm classes, she said. So she did, and they returned; her sister was 15 and brother was 16.

The younger sister lived in a home with other Nxivm members far from the rest of the community. She became the maid for one of the group's high-ranking members, cleaning her house for money and attending Nxivm classes, Daniela testified.

The brother went to live in a home with other older Nxivm members, too, she said.

"I felt like I lost control of them," Daniela testified. "I wasn't the one taking care of them."

Daniela started to tear up when prosecutor Moira Penza questioned her if she ever asked Raniere if he was having sex with her little sister.

Daniela said she noticed her sister became withdrawn and depressed.

When Daniela confronted him, he told her the answer was yes, she said.

"He asked me if I minded."

Now, she says she feels ashamed of her initial reaction.

"I was also feeling kind of jealous. I was thinking, 'Oh, he made he wait until after my 18th birthday, and he's having sex with my sister now,' " Daniela said.

"He said there were some women -- girls -- that were more emotionally mature than others."

Court ended for the day after her testimony. She was led out of the courtroom, hanging her head, her eyes filled with tears.