Here are two links to the Green Book. I read Winn's last night and today. It's very short and a fast read and was intended for Shi'ites. There's a lot of kooky stuff in it that would send any non-Muslim woman into a rage, because of the chauvinism and implication that women are only property.
But... in neither link is there any reference to "thighing". Even if such a practice exists under another word, it's still not in the Green Book. In fact, section 19 states
"To look upon the face and hair of a girl who has not reached puberty, if it is done without intention of enjoyment thereof, and if one is not afraid of succumbing to temptation, may be tolerated. It is however recommended that one not look upon her belly or thighs, which must remain covered."
I'd like to find out more about this but most sites that come up when you google "thighing" have an anti-Muslim agenda. This makes me think that the practice is cultural, not Islamic, but nobody wants to mention that. I'm willing to learn more. However, if the woman in the interview said the practice is mentioned in the Green Book, she'd have to cite chapter and verse because I didn't see it.
http://prophetofdoom.net/The_Little_Green_Book_2_19.Islam
http://infidelsunited.com/greenbook.pdf