Then, according to police, she climbed a tower at an abandoned cement plant and leaped to her death.
Police now believe Rebecca had been bullied for more than a year. On Monday, authorities charged two girls, ages 12 and 14, with aggravated stalking. Deputies arrested the girls and released them to the custody of their parents. The court date has not yet been set.
The 14-year-old girl, whose name is being withheld by PEOPLE because she's a minor, allegedly began taunting Rebecca in the halls of Crystal Lake Middle School in Lakeland, Fla., after the 14-year-old started dating Rebecca's former boyfriend.
According to authorities, Rebecca was "terrorized" by as many as 15 girls on social media. She received messages like "you should die" and "why don't you go kill yourself?"
According to police, the 14-year-old and the 12-year-old, whose name is also being withheld, stepped up the bullying. "Several students corroborated stories of both girls bullying Sedwick ... through name-calling, intimidation, threats to beat her up, and at least one physical fight," the Polk County Sheriff's Office says in a statement.
Although Rebecca switched schools, the bullying continued on social media. After Rebecca killed herself, one of the girls posted on Facebook, "yes, I believed Rebecca and she killed herself I don't give a [expletive]," according to authorities.
Polk County Sheriff Grady Judd addressed the media on Tuesday.
"Words are hurtful," he told reporters. "They are as hurtful – and sometimes more hurtful – than sticks and stones. Ask Rebecca's family."
Efforts to reach the families of the two arrested girls were not successful.