Sometimes, kids do have short term memories. However, especially with girls, I believe they tend to drag bullying out, and it goes on and on and on.
I agree with winnie, let the school handle it at this point.
I would however, make sure there is a police report of the incident on file at your local police department. I don't know if your school's officers are actual police officers. Our districts officers are actual police officers, and one is assigned to each school, and is there all day, everyday.
I hate bullying, and think that threats made should be taken seriously. If there are consequences for bullying behavior, maybe there wouldn't be so much of it. It seems worse in today's society, than when I was a kid in the 70's. Today you can use the internet and cell phone texting to arsenal!
The most important aspect of meetings however, is anonymity. This allows all who enter these rooms to feel safe!