Is Modesty Important in a Home?

AliceGee1 asks: "My 15 year old daughter has never seemed to be self-conscious about her body like most teens, and often wanders around upstairs half dressed or completely naked. If I suggest that she throw something on because of her younger brother (13) she'll say something like 'Well, he already knows what I look like, what's the big deal?' Any advice, or should I not be concerned?"