What does it mean when a girl twirls her hair?

I have been talking to this girl and we get along fine. We joke a lot and are always giving each other "a hard time" and teasing. A few days ago I noticed she checked me out (was looking into my eyes and then she gave my body a "visual sweep" and came back up to meet my eyes) but I didn't think much of it. Today though, we were talking and she was smiling, looking into my eyes and twirling her hair. Is there a meaning behind that or am I thinking too much?
What does it mean when a girl twirls her hair?
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