LAKELAND — Twelve-year-old Rebecca Ann Sedwick briefly stayed with her older sister in St. Petersburg last June. The two got matching bracelets and manicures. Becca got pink. And she opened up to her big sister, Amy Sedwick, 25.Becca showed her sister the self-inflected cuts on her abdomen. She said girls from school were saying she should die.Go kill yourself, her sixth-grade classmates wrote on the Internet. Why haven't you already died?Amy Sedwick told Becca to ignore them, and Becca promised she wasn't cutting herself anymore. She enrolled at a different Lakeland school last month.On Tuesday, Becca, a former cheerleader with silky brown hair, who loved the boy band One Direction and planned to try out for the school choir, killed herself.Her family and Polk County deputies blame months of cyberbullying.Like her mother, who is overwhelmed with questions and regret, Amy Sedwick is replaying those weeks in her mind, wondering what she could have done better. Becca's mother, Tricia Norman, said Friday that she blames herself for not scouring her daughter's phone and computer, where much of the taunting happened without Norman's knowledge.Norman knew girls were pulling Becca's hair and saying mean things about her at Crystal Lake Middle School last spring. She thinks it started over a boy. Becca's mother pulled her out of Crystal Lake and homeschooled her through the end of the year. Becca saw a counselor, and her family thought she had improved.She was making new friends at Lawton Chiles Middle Academy. She smiled easily.When she didn't show up at school on Tuesday, her mother reported her missing.News of Becca's death spread quickly after her body was found Tuesday evening at an abandoned cement plant near her Lakeland home. Facebook support groups popped up, and locals organized fundraisers for funeral expenses.The Polk County Sheriff's Office is investigating and says there could be criminal charges if it finds evidence of online stalking.On Friday afternoon, a steady stream of strangers stopped by a growing memorial at the plant on N Eastside Drive. Trecia Berry, 58, set down a candle, rosary and plaque with the Lord's Prayer. Then she walked back to her truck, sat and cried.Like Becca's family, Berry is heartened by the Lakeland community's outpouring of support for the girl."But where were they when she needed help?" she asked.After Becca's death, Norman saw things she wishes she would have known about earlier.A photo on Becca's Instagram account said "If I went missing, would anybody care?"And Becca had written in a notebook: "Everyday more and more kids kill themselves because of bullying. How many lives have to be lost until people realize words do matter?"To say this week has been a nightmare for Norman would be to put words to something unexplainable. She doesn't know what to do or what to say. She has been talking to reporters, though, hoping to warn other parents.She wants to start some sort of national anti-cyberbullying campaign. She might reply to the congressman who emailed her about writing "Becca's law." A CNN reporter visited her modest Lakeland home on Friday.One in five children are victims of cyberbullying, according to Florida Atlantic University criminology professor Sameer Hinduja, who has written books on the issue. About 15 percent of children have bullied online.Cyberbullying may be a new buzzword, but all it means is that the age-old issue of relentless torment has found a new venue. It is not an epidemic, but it is something parents should be vigilant about, Hinduja said.As bullying took to the Internet, it became unique in a couple ways. Often, a person will say worse things online — things their conscience would not allow them to say face-to-face. Also, cyberbullying can be difficult to escape. With the social media, text messages and smartphone apps, schoolhouse issues can follow children home.Amy Sedwick wonders if her sister was going online and reading the hateful messages at night, when the rest of the family was asleep.Polk County Sheriff Grady Judd said his office has identified at least 15 girls who were involved in Becca's social media circle. The parents of the girls have cooperated with detectives and several cellphones and laptops have been confiscated, Judd said.Norman believes some of those girls are just witnesses. But as for those who are responsible, Norman hopes they go to jail."They knew what they were doing," she said. "And they wouldn't stop. They just stalked her wherever she went."Norman wants parents to do what she didn't — to pay close attention to what their children are doing online and on their phones."Because Becca seemed perfectly happy," she said. "I wish I looked harder. I just thought everything was okay."Times news researcher John Martin contributed to this report. Jessica Vander Velde can be reached at [email protected] or (813) 226-3433.