Well if this report is true (as there is so much 'this Muslim did this that and the other' trend in the media going on) then one has to establish what this ladies contract says about dress code. As the saying goes 'there is always two sides to every story' and it would be important to check out all the facts on both sides. One start would be to analyse the dress code over the history of the establishment. Did it change much?. Was it predominately of one type e.g. smart or revealing?. Of course sleazy dressing will be for sleazy joints and vice versa.
I've seen some bars etc. in the UK and usually the men/women are quite smartly dressed in things like long-sleeved shirts, waistcoats, trousers etc - i.e. what would generally constitue a smart unifrom. That dress they asked her to put on seems more like something a person would go out to party/flirt in - it doesn't conjure up the immediate picture of 'uniform'.
Anyway like I said the case needs looking into deeply especially before making generalisations like "she has no case to sue or not".
Dress codes can be changed at will. One day you can be made to wear a red shirt and brown pants and the next day they can consider blue a better color and make you change.