Why's she act like this?

here's a girl I work with I'm fond of but it's hard to talk to her at work. We've been a little more chatty then normal since I bought her a frappe as a thanks for giving me a energy drink as a pick me up. I've noticed lately she's been brushing her fingers through her hair when she's around me and the other day when I was feeling down she was the only one that noticed and asked if I was okay.
Why's she act like this?
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