A 5-year old from a pet store? She could have some separation issues for sure. Do you know where she came from before the pet store? You will need to be very patient and very loving. But you need to find ways to get her to trust you as well. Journey826 had some good advice surrounding feeding time.
If you share a few more details, more will offer advice. There is a LOT of experience with just about any issue here on YT.
Oh, and WELCOME!!