I know you've got her named... but I did a search on askjeeves.com and came up with a few other Peanuts characters...
Molly Volley -- she was on the vollyball team
Patty (who was different than Peppermint Patty)
Peppermint Patty -- of course!
Violet
Clara
Marcie
Lila - Snoopy's original owner
Loretta -- girl who sold Girl Scout Cookies
Lydia -- Linus had a major crush on her
and finally...
Little Red Haired girl -- she was never named
Here's the link with a whole bunch of Charlie Brown Trivia if anyone is interested....
http://www.peanutscollectorclub.com/peantfaq.txt