"It makes me angry that I'm being punished for bullying and a rapist isn't being punished for raping people," she added.
School officials also told NBC that they were satisfied with Mansmann's three-day suspension as they are required to look into all claims of bullying.
Cape Elizabeth High School also revealed in a statement that the school "has never disciplined a student for advocating for their peers or their views on cultural, social and political matters".
"It is important to understand, however, that when a student's speech bullies another student, we are required by law and by school board policy to investigate and take prompt action."
The 15-year-old told Buzzfeed that she was confused about her punishment of bullying as she did not name the alleged "rapist".
"This person self-identified feeling targeted, so the school took steps to suspend me versus further investigating that self-identification," she said.
Mansmann has since appealed the suspension with the support of her parents, although her school believes they have given her the correct punishment for her actions.