I agree with a previous poster, I wouldn't go to close to the typical/ stereotypical mean girl's names, which is the feeling I get from most of the ones you have listed. I personally imagine a girl with a unisex name that is better for a boy, a really popular 80-90's name, a wacky name as in unexpected, unusual, and then a girl with a name that is popular today, or a sweet name nobody would expect.
Brynn is a good name.
I agree that mean girls don't have stereotypically 'mean girl' names. I knew a mean girl name Megan, which is stereotypical-ish, but that doesn't make all mean girls the sort to have names like 'Tiffany' and 'Charlotte'. I'd stick to a variety, from unisex to decidedly girly to unusual to common. Like a group named Dylan, Kendall, Carolina, Polly, Gertrude, Fiona, and Xyla. Make it realistic.
There is no such thing as a mean girl name. There are mean girls with all types of names. I knew a mean girl named Julie growing up, but I still don't think of Julie as a "mean girl name" because there are all types of Julie's out there. Perhaps you should focus more on a name that was popular in Virginia and Louisiana at the time these girls were born