You can look up the most popular girls' names from the year your characters would have been born AND look by state on the Social Security website, if that would make it feel more authentic.
As a Southerner, though, here are some mean-girl names from area (birth years in the early 80s):
Shasta (yes, like the discount soda)
As a Louisiana girl- some of the "mean girls" at my school (2008 HS grad)
But I also know a lot of girls with these names who aren't mean- For a true southern sounding name, I would go for at Least one unique double-name like, Mary Finn, Mary Brennan, Mary Jo, Mary Hartly, etc.
One "masculine" name- Frankie, Stevie, Bobbie, Jamie, Jordan, Morgan, Blake, Bryn. Duffy, Charlie, Alex etc.
one long classic name- Victoria, Rosemary, Frances, Caroline, Charlotte, Emily, Elizabeth, Georgia, Alexandra, Etc.
and one over the top or cutesy nicknamey name- KK, Cici, Coco, Penny, Lulu, Gigi, Mimi, Mimsy, Khaki, Posie, Tinley, Finley, Deedee, Darby, Libby, Liv, Sunny, Ali, Etc.