The best advice I can offer is to have patience, patience, and more patience. You may want to put an article of your worn clothing under the chair where she hides, so that she can get used to your scent. Also, spend time in the same room near her just talking reassuringly so she becomes accustomed to your voice. You may also want to kneel down on the floor and tempt her with a teaser toy; she just may surprise you and spring out from under her chair to pounce on it! It is a good sign that she does eat and use the litter box. As Spencer mentioned, she probably was feral or abused, so just needs lots of time and love in order to trust people and her new environment. Good luck, don't give up, and let us know of her progress.