Guinea Pigs

Hi, I recently bought a baby guinea pig from petco, I have had her for a week now. She is extremely skittish, she eats and drinks normally, she is healthy, but she is just scared. I bought her a big cage and an igloo but she rarely comes out of the igloo and when she does come out, if you make one little sound she darts right back in the igloo. I dont know how to get her to not be affraid of me. Im not sure if I should take her out of the igloo or if I should let her come out on her own? She seems to be fine when I hold her. How should I handle this?