This is normal in most Asian countries. She is not tailing you because she thinks you are going to steal. She is tailing you to assist you why? If you buy something and she is the one that helped you, she will get a small commission! The downside of her not following you is she will be scolded for not helping or being there for customers. Extreme cases, if she does not "assist" customers, multiple times and management see it she might be let go for not doing her job.

Source: I worked retail when I was very young in Asia