Both girls were charged as juveniles with third-degree felony aggravated stalking. If convicted, it's not clear how much time, if any, the girls would spend in juvenile detention because they did not have any previous criminal history, the sheriff said.
The sheriff's office identified the two girls, but The Associated Press generally does not name juveniles charged with crimes.
The bullying began after the 14-year-old girl started dating a boy Rebecca had been seeing, the sheriff said.
A man who answered the phone at the 14-year-old's Lakeland home said he was her father and told The Associated Press "none of it's true."
"My daughter's a good girl and I'm 100 percent sure that whatever they're saying about my daughter is not true," he said.
At their mobile home, a barking pit bull stood guard and no one came outside despite shouts from reporters for an interview.
Neighbor George Colom said he had never interacted with the girl but noticed her playing roughly with other children on the street.
"Kids getting beat up, kids crying," Colom said. "The kids hang loose unsupervised all the time."
A telephone message left at the 12-year-old girl's home was not immediately returned and no one answered the door.
Orlando attorney David Hill said detectives may be able to pursue contributing to the delinquency of a minor charge for the parents, if they knew their daughters were bullying Rebecca yet did nothing about it.
But it "will be easy to defend since the parents are going to say, 'We didn't know anything about it,'" said Hill, who is not involved in the case.
Perry Aftab, a New Jersey-based lawyer, told AP last month that it is difficult to bring charges against someone accused of driving a person to suicide, in part because of free-speech laws.