Hehe... this thread brings back memories! When I first brought my 8-week old kittens home, as soon as I opened the door of their carrier, they made a beeline for the sofa. They came out VERY cautiously a couple of hours later - but that was only to gobble up the bowl of food I'd put down, then rush back behind the sofa. Funny little things. Don't worry about it, she will come out in time.
And... welcome to the Forum!
And... welcome to the Forum!