Larxene, the Savage Nymph, is number 12 in the Organization, and was originally thought to be the only female in the Organization XIII. She's above Roxas and Xion, the other girl in the Organization, Roxas being XIII and Xion even lower at XIV.
Kingdom Hearts: Chain of Memories[]
Larxene was working with Marluxia to overthrow the Organization XIII, helped by Axel and Vexen who were both secretly against it. Larxene fights with Sora, but loses and claims to Axel, laughing it off, that she was "throwing the fight".