Oh no, poor scaredy pup! I know how hard it can be to build confidence in shy rescues. We sent our anxious girl Luna to ATX K9's board and train program and it was life changing. The dedicated trainers there used 100% positive reinforcement to work on socialization and exposure in a controlled setting. After 2 weeks, Luna came home a totally new dog - coming out from under the bed, seeking attention, and even playing with toys!
Dog Board and Train Program in Austin customized board and train approach helped Luna gain confidence and come out of her shell. I'd highly recommend checking them out for your shy girl. Their force-free training can do wonders for fearful pups. Wishing you the best of luck and pats to your sweet shy pup!