It is simply going to take time. I adopted two pups about 4 years ago who came from a bad breeding situation. They still have some issues around other people. They are fine with me now...but that took a long time.
Just allow her to come to you when she is comfortable and let her grow and learn that she is safe with you at her own pace.
I would definitely not medicate. This is normal behavior for them...poor babies.
Here is a link that might be helpful:
ASPCA - Virtual Pet Behaviorist - Adopting a Puppy Mill Dog
Bless you for adopting this precious baby. The baby steps she takes will be great moments for you to treasure!