This is so hard and so sad for you. I'm sorry. I don't have much to offer that hasn't already been said but I see so many cats just like her coming into the shelter. They are terrified and in time will usually settle down. I feel so sorry for them during that time. It is heartbreaking.
If I were you I would just keep checking on her and make sure you know how she is doing. Keep us posted.
Good Luck.