I took an older cat last summer to add to my "petting zoo" - she hide in the corner in the family room for a week, then lived on the armchair for another 2 weeks. She actually did not leave the family room for almost 4 weeks, then only forays in the night when we were asleep. She would let us pet her when we were in the same room with her, but she was scared of everything. Fast forward, a year later, and she is totally integrated into the household.
Adopted another cat a month ago, he hid in the same corner of the family room for a week also. LOL It is a popular corner. He adjusted much more quickly, about a week and a half, but is still spooky about loud noises and sudden movements.
Like people, they all have their own personalities. Give her time - she will adjust. Just be patient and don't force her to come out. I tried that with the most recent cat because I was being impatient - set us back a few days for him to recover his budding trust in me.