My sister walks around nude.?

She says she wants to be a porn star (and trust me, she could... she looks like Phoebe Cates did in her prime) and if she can't be nude in front of her brother, she can't be nude in front of strangers. It doesn't bother me because I figure hey... she can do what she wants... but at the same time, sometimes it's nice to watch. Should I tell her to stop?

Not at all. She can continue. There is nothing wrong in being nude. Tell her to be nude all the time and in front of everybody without violating the laws. Tell her to visit nude beaches and be nude there. Tell her to do everything in nude.