Girl's Behavior

Why would she avoid looking at me on purpose?

Why would she avoid looking at me on purpose?
During a workers night out a girl I have known for 3 years or so avoided eye contact with me all night. I don't know if she looked at me while when I was not looking at her but she does do this at work now and again.

She did sit at different table as me and when I approached the table and sat many times she acted if I wasn't there, I did do small talk with momentary eye contact but neither of us kept
the talking going. All night I did notice she was talking away, being social with others and being herself.
Why would she avoid looking at me on purpose?
Later that night just before closing time she was up on dance floor with a guy and she hugged him and noticed me looking while going back to her seat she called out to me a nickname and back hugged me while I was sitting down arms around my neck. The nicknaming is new. She said it twice again to me while we waited for taxi and again in taxi and asking if I was okay.

Other points to make regarding her while in work is she does say hi (she did not on night out), does speak to me if spoken to, asks for my help sometimes, banter here and there, fooling around and occasional with others to. She is a sociable outgoing person and can really talk even though she does talk to two guys regularly from work too with eye contact but with me its not as easy flowing with some eye contact here and there, just more of the looking from afar and noticing her looking at me when I am not looking at her.

Questions:

Why would she avoid eye contact all night with me? then suddenly give me a nickname and the back hug?
Why would she avoid looking at me on purpose?
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