My guess is that it's a girl. I'm no expert, but have read that males' tail feathers curl up, and this was true with the ducks I have had. Since it is white, I wouldn't think it was a khaki campbell, would't they be khaki colored?
I certainly am no expert either but here is my educated guess. That looks like a juvenile Pekin / Peking (sp?). If it is indeed a juvenile it would be too young to have the turned up tail feather yet and without that, you can't tell yet whether it is a hen or a drake. Hope this helps.