IMHO, that is flawed logic. I'm not saying that she is a good role model or anything but at the same time...You can't apply the daughter/sister criteria to every female you see. When you first met your wife, did you think, "Ugh! If my sister smiled at me like that it'd be disgusting!"? I doubt it.
Similarly, I doubt your father-in-law was overly glad to see his daughter making eyes at you. But you were happy, right? You didn't say "If I was your father I'd disapprove!"
flawed logic would say that a nude slut or Helen Thomas were the only choices.