The girl was very upset.
One of our sixth grade girls reported that judging from her sent mail folder on Gaggle.net, someone else had been using her account to send messages. The principal was brought in. The guidance counselor, parents and media specialist all met. And even yours truly, the tech director, got involved.
After some discussion, the girl remembered that she had given her username and password to her "very best friend" at another school, and that they were using the e-mail program at her friend's house on the day the messages (which were innocuous) were sent.
The media specialist changed the girl's password. The counselor gave another talk on cyberbullying. The media specialist emphasized security and privacy in her next lessons. The principal learned the kids actually had e-mail accounts. The tech director was happy this turned into a "teachable moment" for all involved.
It is because of incidents like this that I am glad we have always given our students school sponsored e-mail addresses. It allows kids to make "safe mistakes." The girl and probably her classmates got a real-life lesson in protecting one's password and about identity theft without anyone getting hurt.
It's why we need to give kids as much access to Internet resources as we can while they're in school and while there are responsible adults to whom they can turn if there is a problem. How would this have been handled if the girl had only had a Yahoo account and home access?