This girl keeps acting strange around me. Any ideas why?

I have a crush on this one girl I know. But she is at work. So she has some coworkers. But it seems to me she acts more confident when she is around her co-workers (she is nice, more talkative friendlier, etc) but when we are alone she sometimes ignores me. She keep taking glances at me but it is difficult to talk to her if she is doing this.
This girl keeps acting strange around me. Any ideas why?
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