[Always *]

It was a bitch move but like best friend said, justbecuase you feel like it was unfair, it isn't illegal for her to do that since she didn't actually give a reason involving something discriminatory.For all you know someone went over her head and said she can only interview X amount of candidates. Or maybe something DID come up, like one of her kids needs something done during that time, who knows. But in any case, while it is unfortunate as it is its not like she came up to you and said your gender, race, religion, culture, etc are the reasons. I know it sucks, but if she already knew about the break down before, and the other people had good qualifications, and when forced to choose, she might of decided that of the group chosen that maybe you were the one most likely not to be ready to handle the pressure.
I'm sorry it happened to you, but I don't see anything discriminatory. And even if it were, it would be pretty hard to prove. I wouldn't go with the whole suing thing, suing tends to be more an American thing for stuff like that, but I know that you could definitely bring it up in court some how, but nothing would come of it more likely than not cause she could easily just be like "this is why I had to turn her down last minute" and it wouldn't be discriminatory. If you are concerned, you COULD just let her know you were a bit upset you got turned down last minute and just ask for the reason why YOU were unselected, and NOT the reason why she had to downsize