Assume the Teacher is Unaware
Some parents are angry that bullying has gone so far without a teacher's intervention. Most bullies are subversive, however, and torture their victims out of view of authorities. This is especially true of cyberbullying. As you enter the meeting, assume the bullying will be as surprising to the teacher as it was to you.
Also, don't assume the teacher knows how to work with parents on an emotional level. Except for grade discussions, teachers are rarely trained on teacher-caregiver relations, and inexperienced teachers might be nervous. It's best to walk into the meeting with no assumptions.