The Devil Wears Prada

Andrea (Anne Hathaway) is an aspiring journalist fresh out of Northwestern University. Despite her ridicule for the shallowness of the fashion industry, she lands a job "a million girls would kill for," junior personal assistant to Miranda Priestly (Meryl Streep), the icy editor-in-chief of Runway fashion magazine. Andy plans to put up with Miranda's bizarre and humiliating treatment for one year in hopes of getting a job as a reporter or writer somewhere else.
At first, Andy fumbles with her job and fits in poorly with her gossipy, fashion-conscious co-workers, especially Miranda's senior assistant Emily Charlton (Emily Blunt). However, with the help of art director Nigel (Stanley Tucci), who lends her designer clothes, she gradually learns her responsibilities and begins to dress more stylishly to show her effort and commitment to the position. She also meets attractive young writer Christian Thompson (Simon Baker), who offers to help her with her career. As she spends increasing amounts of time at Miranda's beck and call, problems arise in her relationships with her college friends and her live-in boyfriend Nate (Adrian Grenier), a chef working his way up the career ladder.
Miranda is impressed by Andy and allows her to be the one to bring the treasured "Book," a mock-up of the upcoming edition, to her home, along with her dry cleaning. She is given instructions by Emily about where to leave the items and is told not to speak with anyone in the home. Andy arrives at Miranda's home only to discover that the instructions she received are vague. As she tries to figure out what to do, Andy begins to panic. Miranda's twins (Caroline and Cassidy, played by Colleen and Suzanne Dengel, respectively) falsely tell her she can leave the book at the top of the stairs just as Emily has done on many occasions. At the top of the stairs, Andy interrupts Miranda and her husband having an argument. Mortified, Andy leaves the book and runs out of the home.
The next day, Miranda tells her that she wants the new unpublished Harry Potter book for her daughters and, if Andy cannot find a copy, she will be fired. Andy desperately attempts to find the book, nearly gives up, but ultimately obtains it through Christian's contacts. She surprises Miranda by not only finding the book but having copies sent to the girls at the train station, leaving no doubt that she accomplished Miranda's "impossible" task, thus saving her job.
One day, Andy saves Miranda from being embarrassed at a charity benefit, and Miranda rewards her by offering to take her to the fall fashion shows in Paris instead of Emily. Andy hesitates to take this privilege away from Emily but is forced to accept the offer after being told by Miranda that she will lose her job if she declines. Andy tries to tell Emily on her way to work. However, Emily is hit by a car and Andy has to break the bad news while visiting her in the hospital.
When Andy tells Nate she is going to Paris, he is angered by her refusal to admit that she's become what she once ridiculed, and they break up. Once there, Miranda, without makeup, opens up to Andy about the effect Miranda's impending divorce will have on her daughters. Later that night, Nigel tells Andy that he has accepted a job as Creative Director with rising fashion star James Holt (Daniel Sunjata) at Miranda's recommendation. Andy finally succumbs to Christian's charms and, after spending the night with him, learns from him about a plan to replace Miranda with Jacqueline Follet as editor of Runway. Despite the suffering she has endured at her boss's behest, she attempts to warn Miranda.
At a luncheon later that day, however, Miranda announces that it is Jacqueline instead of Nigel who will leave Runway for Holt. Nigel remarks to a stunned Andy that, though disappointed, he has to believe that his loyalty to Miranda will one day pay off. Later, when Miranda and Andy are being driven to a show, she explains to a still-stunned Andy that she was grateful for the warning but already knew of the plot to replace her and sacrificed Nigel to keep her own job. Pleased by this display of loyalty, she tells Andy that she sees a great deal of herself in her. Andy, repulsed, says she could never do that to anyone. Miranda replies that she already did, stepping over Emily when she agreed to go to Paris. When they stop, Andy gets out and throws her cell phone into the fountain of the Place de la Concorde, leaving Miranda, Runway, and fashion behind.
Some time later, Andy meets up with Nate, who is moving to Boston because he got a new job as the sous chef of a restaurant. They agree to start dating again and see what the future holds. The same day, Andy is interviewed and is accepted to work at a major New York publication company. It was Miranda who insisted that they hire Andy, despite that she didn't work for her a full year, but the company would be "the biggest idiots" if they don't. Andy calls Emily and offers her her Paris wardrobe and the two leave on good terms. Andy passes the "Runway" office building and sees Miranda get into a car. Andy gives a wave, but Miranda does not acknowledge her. Andy is used to this and instead walks further into the crowd. Once inside the car, however, Miranda smiles and then orders her chauffeur to drive.

Question: Why does Andy panic?
Answer: Instructions are vague