Buff Orpington pullet or roo?

I am completely new to chickens. These four buff orpingtons are our first. They are 11-12 weeks old now and are all supposed to be pullets. I am becoming a little suspicious that one of my lovely ladies may not be a lady at all, but I have no experience, she may just be a bit bossy. She started out as the sweetest in the bunch, but now doesn't want to be handled at all. She puffs up to the other girls, but doesn't peck them, and will come roost on my back if she wants to. Any expert opinions appreciated. We will have to eat him if it starts crowing.[/IMG]