Shy girls, how do you show affection?

I've been trying to figure out this girl for a while. She is shy and quiet but playful with people she knows. With me she kind of gets nervous and quiet. I have noticed that most of the time we talk we are either making fun of each other or arguing. People around us crack up ALL the time when we are "fighting" (we do dish out some great punishment). Sarcasm is great between us and she seems to enjoy to see me "suffer" as in if other people make fun of me she starts laughing at me and agreeing with them or if I say how I tripped and fell, she tells me she would've loved being there so she could laugh or she is just mean to me. She always has a smile when we talk and when she is "mean" she just stares at me but then starts cracking up or looking away. Could there be anything here? I think its funny a quiet girl could muster the courage to be like that to me, especially since I'm "well liked" in our circle.
Shy girls, how do you show affection?
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