The fact that it's religiously-related is irrelevant.
What if my religion believes that women should be 100% subservient to men? Does that mean that as a store salesperson that I get to tell female customers what to purchase?
What if I want to carry one of these religious knives?
Or maybe I like dressing like this:
A expectation of dress is exactly that. Freedom of religion means freedom to practice your own, but should equally mean that others shouldn't have to pay you for practicing yours.
If you tell them all that, and they say yes, I still blame them, not you. The lie that it's ok comes from them.
Here, let me put it in a puds-like woman hater language.
If a girl meets a guy who is an unapologetic asshole....and she dates him either a) thinking she will be ok with it or b) thinking she can change him....when things go foul because he's an unapologetic asshole who doesn't want to change, do you blame the guy for not conforming to being a good boyfriend, which he never promised to be, or do you blame the girl for knowing what she was getting and banking on his possible willingness to change and be the guy she wants him to be?
This has nothing to do with religion for me. You simply don't hire someone who can't do the job, even for PR. Hiring her and then trying to change her is more stereotypical woman behavior than her being hired on an honest plane where her dress was known ahead of time, and her taking issue with it suddenly being a problem.