I see you added some after I quoted you...
That doesn't make sense...You said earliar that
"The Qur'an tells them to wear one in the presence of all men who are not fathers, brothers or spouses."
Why would the husband require his wife to wear one to keep from sinning if she isn't required to wear one in his presence?
But the husband requiring one is not the norm, so I can't say why Cindy's friend was required by her husband to do so considering she isn't religiously obligated to wear one for him. More likely is that he requires her to wear one so that other men do not sin by thinking/acting lustfully towards his wife.