A teenager in Maine is fighting a suspension after warning classmates about an alleged rapist at school. But school officials said her warning amounted to bullying.

Aela Mansmann, 15, is a sophomore at Cape Elizabeth High School outside Portland. She and two other students were suspended for three days after posting a note reading, "there's a rapist in our school and you know who it is."

"If I'm being punished, will other people fear being punished as well," Mansmann told CBS News.

According to the school principal, Mansmann was suspended because her notes made a male student feel bullied, targeted, unsafe.

Aela Mansmann with the note, reading: "There's a rapist in our school and you know who it is." Aela Mansmann via WGME

"I was pretty disappointed that my administration then decided to investigate the claims," Mansmann said.

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She is a passionate advocate on issues of sexual assault, organizing a youth summit this year and speaking out at a school board meeting in June.

According to the National Sexual Violence Resource Center, one-fourth of girls and one-sixth of boys will be sexually abused before their 18th birthday. The ACLU of Maine is now asking a federal court to stop her suspension.

"We are really concerned that schools are trying to silence students instead of raise these issues up," said Alison Beyea, ACLU Executive Director of Maine.

Mansmann said her note was not an accusation about a specific rape, but a general criticism of the school's culture, which she said, does not openly address ways to prevent abuse.

"This is the least reported crime in the U.S.," she said.

Cape Elizabeth High School has not responded to CBS News' requests for comment citing the pending litigation.