Would it be ok to specify that you're looking for a Christian on a dating site, or is that discriminating, too? If she had a couple of long-haired dogs, would it be ok to specify that she is looking for a dog-lover? Or would that be discriminatory against people who hate dogs? And would a dog-hating or allergic roommate shoved down her throat by the state then be able to make her get rid of the dogs? This is so obviously ridiculous on its face that I can't believe someone hasn't had the good sense to throw it out. You can't overtly offer for sale or rent to a particular class. But that is not what she was doing. She was looking for a roommate, who will have no protection of a lease if this woman owns the house.
Of course the way around it is instead of describing the roommate you are looking for, describe yourself: Single woman with strong Christian beliefs, whose best friend and savior is her Lord Jesus Christ, is looking for a roommate....... and just scare off those you don't want.