Oh my goodness, she's adorable!
Give it some time, she'll be running around like a maniac before you know it. Cats like routine, and hers has just been turned upside and inside out. Hang out with her, talk to her, give her some treats, and most of all, be patient. Like 14+ mentioned, keep litter/food/bedding all in the one room so that it's her safe-haven until she feels more confident.
Originally Posted by CatSTAR
Also would it be a factor that she had a sister and the fact that she got separated from her.
Any possibility you could also adopt her sister? Cats really do like the company of other cats, especially siblings. In fact, some shelters won't even let you adopt a kitten unless you take 2. It's good for their social development, gives them more exercise, and provides them with company when you aren't home. Plus, you can't beat the entertainment value of 2 kittens playing.