A cat will hide for all sorts of reasons, whether it's the sudden appearance of the cat carrier (indicating an upcoming car trip), or the frightening noise of the vacuum cleaner. Some cats simply do not feel sociable while you have company visiting (human or animal). Unless you are in a hurry to make that veterinarian appointment or to catch a flight, leave your cat alone for a little while. She will probably come out later when she's feeling more sociable. However, seek out your cat if she misses the next meal or will not come out of her hiding place for a longer period of time-it could be an indication of illness.
The best way to find a hiding cat is to ask yourself this question: "If I were a cat, where would I hide?" Start with these favorite spots: