Problems with new cat?

We just got a new Calico from the local SPCA and she is absolutely petrified. I know thats normal at first, but we brought her home and opened the carrier in which she then hopped out quickly and sat on the second shelf of our book case. To make a long story short, she was hiding behind the couch and hadn't eaten anything for about 2 days, so I called the SPCA and they said to put her in a room by herself with her box, food, toys, bed, etc... so we tried to nicely grab her and she freaked and it turned into a kind of rodeo in which she then peed on the rug (after more than a day of not using the box) and we got a hold of her and put her in the other room. So, she is still not eating (day 2.5-3) and hasn't used the box at all. She is hiding in a corner by the cabinet and hasn't moved all day. I'm worried that she may become dehydrated or maybe emaciated in the future due to not eating for God knows how long. Are there any experienced cat people out there that have any advice or ideas as to what we can do for her to make her feel more calm and at home?