Nichols, now a star at the University of Oklahoma, said Tuesday she was joining other gymnasts who have told their stories about Larry Nassar to "bring about true change."
"Up until now, I was identified as Athlete A by USA Gymnastics, the US Olympic Committee and Michigan State University. I want everyone to know that (Nassar) did not do this to Athlete A, he did it to Maggie Nichols," she said in a statement.
Nassar will be sentenced next week on state charges. In November, he pleaded guilty to seven counts of first-degree criminal sexual conduct
and admitted to using his position to sexually abuse underage girls. Three of those charges are related to victims who were under age 13.
More than 140 women and girls have accused him of sexual misconduct, including several American gymnasts on the "Fierce Five" team that won gold at the 2012 Olympics.
Nassar was the team doctor for USA Gymnastics through four Olympic Games, and he worked at Michigan State University from 1997 to 2016 as an associate professor and as the gymnastics and women's crew team physician.
Nichols, 20, said she and a coach reported the abuse to USA Gymnastics in 2015, a few years after Nassar began treating Nichols for a back injury.
"I trusted what he was doing at first, but then he started touching me in places I really didn't think he should," she said, saying the abuse happened numerous times, starting when she was 15 years old.
Nassar also sent her Facebook messages complimenting her looks, Nichols said. In 2015, a year in which Nichols was a member of Team USA's world championship squad, a coach overheard Nichols talking with a teammate about Nassar's conduct and they went to USA Gymnastics officials, Nichols wrote.
Nichols' statement is similar to the information attributed to Jane A68 Doe in a lawsuit filed by Rachel Denhollander and 74 anonymous plaintiffs (including Nichols).
The lawsuit alleges the sexual abuse involving Nichols happened 20 times at a training center operated by Bela and Martha Karolyi.
An attorney for Nassar, Matthew Newburg, told CNN Tuesday night he had no comment on Nichols' allegations.
USA Gymnastics released a statement Tuesday saying it "admires Maggie Nichols' bravery and encourages our athletes and others, like Maggie, to share their personal experiences with abuse. We are sorry that any athlete has been harmed during her or his gymnastics career."
The organization, the governing body for the sport in the United States, said it "reported Nassar to the FBI in July 2015 and to a different FBI office again in April 2016."
USA Gymnastics said last year it would implement 70 policy change recommendations
from an independent investigator.
Last year as a freshman, Nichols was a three-time All-America and a co-national champion on the uneven parallel bars. Oklahoma won its third team title in the past four seasons.
"I would like to let everyone know that I am doing OK. My strong faith has helped me endure. It is a work in progress," she said.
Two-time Olympian Aly Raisman backed her former teammate.
"I support you @MagsGotSwag12 proud of you for sharing your story. I stand with you. I know this is not easy but I know you are incredibly strong. We will get through this together!" she tweeted.
Raisman also has said
she was a victim of Nassar.
Nichols' attorney, John Manley, said she is focusing on the next NCAA season, which begins for Oklahoma on Monday. Her family will help her crusade for change in the sport.
"It's important that those who failed Maggie and so many other girls be held accountable," Manley said.
Nassar also pleaded guilty last year in federal court to receiving child pornography in 2004, possessing child pornography from 2003 to 2016, and destroying and concealing evidence in 2016 as he was under investigation, according to the US attorney's office for the Western District of Michigan.
He was sentenced to 60 years in prison.