that Peanuts girl character who calls another girl, "Sir."

It was also standard in Star Trek: Deep Space Nine to refer to officers as sir irrespective of the officer's sex. Probably in other Star Treks of that vintage, too, but DS9 was the only one I watched with any regularity. Ain' nothing particularly sex specific about the term other than the minor fact that it stems from a Latin masculine form of an adjective.