I would imagine that 'my pretties' is a specifically Amazon military thing, similar to how drill sergeants will call their men 'you maggots', or 'you horrible little man'. In a culture that consists entirely of beautiful women who pride themselves on their strength and physical prowess, having attention drawn to their more stereotypically feminine aspects is probably a mild form of insult - 'beautiful' is probably all right, but 'pretty' sounds like the sort of thing you'd tell a little girl.