I see what you're saying about the camera conciousness but she is fairly new. I'm sure if Gemma and co. tried to ham it up they'd come across as kinda camp as well. You're also right about Jessica. She used to dance and moves like she has great body control.
However, calling what Gemma and co. do "reserved elegance" is a bit much. They're typical young girls, albeit beautiful young girls, thrust into the spotlight so they're going to act a little shy. But the idea that their demure nature somehow translates to "elegance?" I'm not completly convinced. . .I think Gemma's stunning though...