My daughter works at a hospital. She put in for her vacation months ago, and it was approved for her to take a weeks time. She has made plans with her family to fly to Disney, and to stay the entire time of her vacation, returning on Saturday after

My daughter works at a hospital. She put in for her vacation months ago, and it was approved for her to take a weeks time. She has made plans with her family to fly to Disney, and to stay the entire time of her vacation, returning on Saturday afternoon. Today, they have told her that she is only receiving 3 days vacation and she is to be at work at midnight on Friday, the day before her plane tickets are for. She is all upset, and frankly I don't blame her. Do they have the right to do this, and if she doesn't come back in time to work, (which she isn't) can they fire her?