I think you are misreading Jessica’s discomfort around you as social anxiety. She may have gotten the hint that you like her or that you seem over-eager in getting to know her, and she is acting nervous because it makes her uncomfortable. A reason her mouth could have been shaking is because she was unexpectedly alone with you (a male) late at night at work. Or she was simply startled because she didn’t realize you were there. For whatever reason, she feels uncomfortable around you and is sending you a lot of signals that she doesn’t wasn’t to answer your questions. Maybe you could practice socializing with people who seem more receptive than she does?