Girls, When a girl knows a guy and gets along well with him, what makes her go shy/nervous towards him?

[ando90]

This girl i like seems to have gone nervous/shy around me. We actually talk a lot at work, but for some reason she is so mysterious with me. But then she got concerned when she thought I had left my job. I wasn't even at work that day when she thought I quit. But one of my friends at work said she got all concerned. Yet alone when I'm around she is mysterious and seems little nervous/shy with me. I don't get it

[cryscrys1]

Try to talk to her message her anything
She is probably an introvert / shy
I’m one so if you have realized she is shy try to initiate

[ando90]

She likes talking to me in person. She even called out my name and waved to me when she saw me for the first time in a while. She doesn't do that to anyone else at work. When I talk to her she plays with the collar of her shirt and name badge everytime we talk

[cryscrys1]

Do you have her number? Try to message her it can be anything. How was your weekend etc

[ando90]

The only thing is she didn't use to be shy with me. Now she has turned shy on me for no apparent reason