I think that one of the cruelest forms of bullying for middle school girls is the silent treatment. All girls want to fit in at this age, and this type of bullying is a clear statement of exclusion.
This happened to me when I was a kid, and I found that the best way to deal with it was to act like it didn't bother me. When the group that was giving me the silent treatment realized I didn't seem to care, they came around and began talking to me again. However, by this time, I had come to realized that they really weren't my friends and that I didn't want to socialize with them anyway.