Daisy Coleman, a sexual assault victim advocate and subject of the Netflix documentary Audrie & Daisy, has taken her own life, according to her mother.
Ms Coleman, 23, was 14 when she alleged she was raped at a party in 2012 in Maryville, Missouri.
Her case drew national attention as she spoke of being bullied after the incident, but the charge against the teenage boy she accused was dropped.
She was reportedly found dead after her mother called police to check on her.
"She was my best friend and amazing daughter," her mother, Melinda Coleman, wrote on Facebook.
"I think she had to make it seem like I could live without her. I can't.
"I wish I could have taken the pain from her! She never recovered from what those boys did to her and it's just not fair. My baby girl is gone."
Ms Coleman alleged she was assaulted while intoxicated by a 17-year-old boy, Matthew Barnett, at a house party in January 2012, when she was 14.
Her mother said she found her daughter the next morning, left outside on the porch, with wet hair and wearing just a T-shirt and sweatpants in sub-zero temperatures.
Barnett was charged with felony sexual assault, but the case was eventually dropped. Ms Coleman's family argued this was due to the local political connections of the boy's family.
Barnett pleaded guilty to a lesser charge of child endangerment, arguing his sexual intercourse with Daisy had been consensual.
Ms Coleman's case sparked national discussions over teenage rape cases in the US justice system as well as victim blaming and bullying. Ms Coleman and her family eventually moved out of Maryville after threats and harassment in school.
She was featured in the award-winning 2016 Netflix documentary Audrie & Daisy, which highlighted the bullying faced by teenage assault victims.
The other girl in the film, Audrie Pott, took her own life in September 2012, days after she was sexually assaulted.
Ms Coleman helped co-found the SafeBae (Before Anyone Else) non-profit organisation to help prevent sexual assault in schools.
In a statement on Wednesday, SafeBae said the team was "shattered and shocked by her passing".
"She had many coping demons and had been facing and overcoming them all, but as many of you know, healing is not a straight path or any easy one. She fought longer and harder than we will ever know."
The statement added that Ms Coleman had worked to help young survivors, and would want them "to know they are heard, they matter, they are loved, and there are places for them to get the help they need".
From Canada or US: If you're in an emergency, please call 911
You can contact the US National Suicide Prevention Lifeline on 1-800-273-TALK (8255) or contact the Crisis Text Line by texting TALK to 741741.
You can call the UK Samaritans Helpline on 116 123 or visit samaritans.org.